So who is going to triumph? Most experts expect a tough, close fight while giving Mayweather the edge, but it is safe to say that when it comes to these two boxing superstars, anything can happen in that ring on Saturday night.
Here's how the media and boxers, past and current see "The ONE":
Mike Tyson, Former World Heavyweight Champion (Mayweather): "I've only seen Canelo fight twice -- against [Josesito] Lopez and [Austin] Trout. Trout gave him some trouble and he isn't as experienced and as technically skilled as Floyd is. Floyd stays in tip-top shape and is a very relaxed fighter. He is at his peak. It's going to be hard for anybody to beat Floyd now unless he doesn't train. Floyd has transcended the game so much that the best fighters out there now try to emulate his style. Floyd wins by a decision.''
Lennox Lewis, Former World Heavyweight Champion, (Mayweather): "Mayweather will win because of his speed and experience. He's been at this level before so that will also be an advantage. He's the best until proven otherwise. Canelo is talented, young, strong and dangerous ... makes it all the more exciting.''
Bernard Hopkins, IBF Light Heavyweight World Champion: "This fight is 50/50. It can go either way. Floyd has speed and wisdom. Canelo is strong and big. This is a massive fight and the outcome will impact both of their careers in a major way."
Paulie Malignaggi, Former World Welterweight Champion, (Mayweather): "You can't count Canelo out because he's a natural junior middleweight so he has a chance. But at the end of the day it's Mayweather winning on points.''
Carlos Molina [who is challenging Ishe Smith] (Mayweather): "At first it looks like Mayweather's experience and speed will be too much for Canelo. But then you think about it and Canelo is young and strong. This is boxing. You just never know. I would say at this point it is 60-40 Mayweather."
Chris Arreola, Heavyweight Contender (Mayweather): "He's got the experience and he's been in a lot of big fights before. That is not to say Canelo hasn't, but Mayweather has been in more and knows what to do in a fight of this magnitude. I think Canelo took this fight two fights too soon. Mayweather by decision.''
Zab Judah, Former World Champion (Mayweather): "Mayweather is too fast and has great timing. I just don't see Canelo hitting him. I don't see Canelo being able to do anything to Floyd."
Seth Mitchell, Heavyweight Contender (Mayweather), "Floyd's boxing IQ is just too great. His offense, defense is just too good.''
Rafael Marquez, Former Two-Division World Champion, (Canelo): "The winner of this fight is the boxer with the most intelligence and power ... and I hope it is going to be Canelo.''
Gary Russell, Jr., Undefeated World-Ranked Featherweight: (Mayweather): "In order for Floyd to beat Canelo, he has to keep Canelo on the outside and outbox him and pot shot him. Floyd needs to make it clear that he's landing the cleaner and more effective punches. For Canelo to win, he needs to make the fight ugly and finish his combinations with a hook. He has to make it ugly and rough for Floyd. If Canelo makes it close, he will win.''
Rau'shee Warren, Three-time U.S. Olympian and Bantamweight Prospect, (Mayweather):"Floyd's a chameleon; he can adapt to any type of style in the ring. Canelo is a one-dimensional fighter; he wants to bang it out and brawl. He thinks that hitting Floyd in the arms will wear him down, and I think he needs a better strategy than that. It's going be a good fight though. Canelo is young and hungry, he's going to come to fight, but he's going to see that Floyd's a teacher in there. I have to go with Floyd, but I'm ready to see what Canelo brings to the table.''
Marcus Browne, 2012 U.S. Olympian and Light Heavyweight Prospect, (Mayweather): "I think Floyd wins the fight in 10 rounds because he has a huge edge in experience and he's a better all-around fighter than Canelo.''
Daniel Jacobs, Middleweight Contender,"I think the fans will be the real winners on this whole card. I don't really like making predictions but I know that in a card of this magnitude, the fans will come out on top. All of the fighters have to be at 100 percent because if at any given second a mistake is made that might be the deciding factor in both fights.''
Lucas Matthysse, Interim WBC Super Lightweight Champion, "If the fight goes the distance then Floyd Mayweather will win but if Canelo Alvarez fights intelligently he could win the fight.
Adrien Broner, Floyd Mayweather will win by KO in the late rounds.
Tim Dahlberg, Associated Press, (Mayweather): "Floyd will benefit from the short layoff between fights. I think he will be sharper and stronger. Canelo will have trouble getting to 152 pounds, then have trouble catching Floyd all night. I see an easy unanimous decision and, of course, a huge payday for Floyd.''
Steve Carp, Las Vegas Review-Journal (Mayweather): "Mayweather is too experienced and too sharp for Canelo. If they fought two years from now Canelo would probably win, but right now Mayweather is the superior boxer. Mayweather by unanimous decision.''
Bob Velin, USA Today, (Mayweather): "Experience will be the difference. Mayweather is used to being on the world's biggest stage; Canelo is not. And, of course, Mayweather is by far the superior boxer. And this will be a boxing match, not a slugfest. Mayweather wins a unanimous decision.''
Lance Pugmire, Los Angeles Times, (Mayweather): "Mayweather Jr. is very well facing the strongest fighter he's ever gone against in Mexico's 'Canelo' Alvarez. But to know Mayweather is to understand he reasons with perhaps the most astute boxing mind in the world. Whether it be Alvarez's youth, his recent stamina issues or the fact that Mayweather's sharpness is enhanced in taking his shortest layoff in more than a decade, believe he knows he'll win this one, too, likely by decision, and improve the number next to his cherished zero in the loss column to 45.''
George Willis, New York Post, (Mayweather): "Mayweather wins by decision based on his experience in the big moment. He's the master of adjustments which he'll likely need to do against the young and hungry Alvarez. Alvarez has got to get to Mayweather's body to have a chance. If he does, Floyd will have to protect his ribs, which could expose his chin.''
Kevin Iole, Yahoo, (Mayweather): "Mayweather will see all of Canelo's punches and Floyd rarely gets hit by punches he sees. As long as he doesn't get caught, I think Floyd easily outboxes Canelo and wins a big (unanimous) decision.''
Dan Rafael, ESPN, (Mayweather): "Mayweather will be super-sharp, having just fought in May, and that's bad news for Alvarez. Mayweather wins a convincing decision after a few tough early moments.''
Gordon Marino, Wall Street Journal, (Mayweather): "I don't think Alvarez will be able to cut the ring off on Mayweather. I also think Canelo will be an easy target for righthand counters. Mayweather wins by decision.''
Mark Whicker, Orange County Register, (Mayweather): "Mayweather by decision, because it's hard to see Canelo doing something no one else has ever done.''
Matt Breen, The Philadelphia Inquirer, (Mayweather): "Nope, Canelo is not the one. Until Floyd begins to show signs of slowing down, it's tough to pick against him. He'll outwit Canelo and force him into his fight, avoid his power and drag him to a decision. Floyd wins unanimously.''
Jose Luis Camarillo, Esto Newspaper, Mexico (Canelo): "In a very close fight,Canelo will win a split decision and Oscar will announce a rematch immediately. Canelo is fast and strong and will impose his strength on Mayweather by connecting with good shots to the body and to the head.''
Rene Umanzor, Record Newspaper, Mexico: "I think the fight will be a draw. Canelo has enough boxing skills to confuse and complicate matters for Mayweather. Youth and power are also on his side, However, Mayweather has all the experience, a very difficult style and a great, almost perfect defense. But I don't think he's going to have an easy night.''
Robert Morales, Los Angeles News Group, (Mayweather): "I'm going with Mayweather via decision because I believe he remains the top pound-for-pound fighter in the world, and I'm not convinced Alvarez will be the one to hand him his first loss. The combination of Mayweather's right cross and his sterling defense will get the job done.''
Oswaldo Príncipe, La Nacion, Argentina, (Mayweather): "Mayweather is getting old but he's very smart and still has his strength. Canelo is very young and hasn't incorporated a lot of new techniques to his style. Mayweather wins on points.''
Diego Martínez, Reforma Newspaper, México: "This is a fight where Canelo can surprise the whole world of boxing. I can see Canelo knocking Mayweather down and finishing him by knockout, but I can also see a controversial decision if the fight goes 12 rounds, probably a split decision for Floyd.''
Lem Satterfield, Ring Online, (Mayweather): "In what I believe will be his most difficult fight since the early rounds of Ricky Hatton, the entire Oscar De La Hoya fight and the first two rounds of Shane Mosley, I see Mayweather pocketing enough rounds to win a close but unanimous decision over Canelo Alvarez.''
Matthew Aguilar, El Paso Times, (Mayweather): "Look for Canelo to come out fast and try and hurt Mayweather early. He'll press the action, attempt to pin Mayweather on the ropes and attack to the body -- with moderate success. Mayweather will get caught a few times, but will otherwise escape unscathed. By round three, Mayweather will have found holes in Canelo's defense, and by round five, he will be landing clean, hard shots. He will win most of the remaining seven rounds with crisp counterpunching, speed and boxing skills, while exposing Canelo's inexperience. Mayweather takes a unanimous decision.''
Alberto Henriquez, Producer, CNN Latino, (Mayweather): "In my opinion, Floyd Mayweather will win the fight. Floyd has demonstrated that he is a master in the art of 'reading' his opponent and adapting to his style while being virtually untouchable. I don't think Canelo, although very good, has what is necessary to beat Maayweather. 'Money' will win the fight."
Bernard Fernandez, The Ring/SweetScience.com, (Mayweather): "Mayweather Jr. might be the Lion in Winter -- OK, make that the Lion in autumn; he's still a kid compared to, say, Bernard Hopkins -- but at 36 he's a cagey, smart king of ring beasts. Canelo Alvarez has youth, size and strength on his side, but his relative lack of experience in bouts of this magnitude will prove the difference. 'Money' takes another victory to the bank, via unanimous decision.''
Damian Calhoun, Orange County Register, (Mayweather): "Mayweather is facing a bigger, younger fighter, who could have his moments in the ring. I don't expect this to be an easy night for Mayweather, but I do expect him to win by unanimous decision, by utilizing his speed and defense.''
Ron Lewis, The Times Of London, (Mayweather): "Alvarez has the size and strength to cause Floyd some problems, but Mayweather is smart enough to get through any awkward moments and pull clear in the second half of the fight to win a decision.''
Mike Rosenthal, Ring Online, (Mayweather): "The biggest fight of the year is also one of the easiest to predict. Canelo Alvarez is young, strong and improving, which should work in his favor when he fights Floyd Mayweather Jr. However, the Mexican has neither the skills (natural or learned) nor experience to beat a fighter of Mayweather's ilk. Alvarez will fight hard but leave the ring frustrated and the loser of a one-sided, unanimous decision.''
Carlos Gonzalez, Primera Hora, Puerto Rico, (Mayweather): "This is going to be a great, great fight for the fans from the opening rounds. Canelo can and will pressure Mayweather, but Mayweather will impose his speed and experience and win a unanimous decision''
Alfredo Berrios, ESPN Deportes, (Canelo): "The power and physique of the Mexican fighter will be among his keys to victory. Even though Mayweather has the experience and finesse advantage, Canelo will not allow him him to do his hit and run routine, and Canelo's youth will let him complete what Miguel Cotto couldn't in 2012."
Kieran Mulvaney, ESPN.com, (Mayweather): "Mayweather is too fast, too skilled, too good. As usual, he may take a few rounds to size up Alvarez, but he'll be moving while he does it, not giving Alvarez a chance to land any telling blows. Once he starts to time him, don't be surprised to see Mayweather fire a few combinations from the pocket as he dominates the second half. Mayweather wins a unanimous decision.''
Lyle Fitzsimmons, CBSSports.com, (Mayweather): "Canelo is a big, strong kid who can punch and sell tickets. And I'm sure Oscar would like nothing better than to see him beat Mayweather into a fine dust. But I just don't see it. The kid barely got past Austin Trout (I had Trout winning by a point) and he'll find out fairly quickly that Mayweather is by no means Austin Trout. Mayweather by TKO 10.''
Doug Fischer, THE RING magazine, (Canelo): "Mayweather is hands down the best welterweight on the planet but on Sept. 14 he will fight a middleweight at a 152-pound catchweight. I don't think having to sweat off the extra two pounds will drain or slow down the 23-year-old junior middleweight champion, who has a higher ring IQ than he's given credit for. I think Alvarez will land the harder, more effective punches in a tit-for-tat boxing match. He might even score a knockdown. Alvarez takes a close unanimous decision.''
Claudia Trejos, ESPN Reporter, (Mayweather): "No easy fight and anything can happen. I do remember nobody gave credit to the young Oscar de la Hoya against the seasoned Julio Cesar Chavez in 1996. Everything is possible in boxing.''
Keith Idec, The Record, Woodland Park, NJ)/BoxingScene.com, (Mayweather): "Facing a younger, legitimate junior middleweight, Mayweather must stay off the ropes, keep a much slower Alvarez moving and use his legs the way he did to dominate Robert Guerrero. If he does those things, Mayweather is just too smart, too skilled and too effective defensively to lose this fight. Mayweather by unanimous decision.''
Leighton Ginn, Desert Sun, Palm Springs, Calif.: (Mayweather): "As good as Canelo is, and despite the major improvements he's made, it's a quantum leap when you face Mayweather. Experience counts, and Floyd is the best on the big stage. He wins a unanimous decision.''
Jake Donovan, BoxingScene.com, (Mayweather): "I'm going way against the grain on this pick, and will expect a version of Floyd similar to the one that faced and drilled Ricky Hatton into Bolivian. I don't see Alvarez being competitive for very long, with Floyd picking him apart in the second half before finishing him via attrition and/or cuts. Mayweather wins by TKO 11.''
Jose Luis Sánchez Pando, HOY Newspaper, Chicago (Mayweather): Mayweather will win a decision.''
Alejandro Rodríguez de la Cruz, El Universal Newspaper, Mexico: "I've got a split decision or a draw. Canelo Alvarez is looking better and better in every fight, and he's fighting in his own division. I know 'Money' Mayweather possesses speed and savvy even though he is 36 years old. But to go up to 152 pounds is going to be tough for him.''
Armando Alvarez, Telemundo Network, (Mayweather) -- "THE ONE is one of the most highly anticipated fights in a long time. When non-boxing fans are asking me about this bout, it speaks volumes as to the magnitude of this event. Canelo' is young, strong and determined. He has underrated boxing skills and will give Mayweather trouble early. Floyd's superb defense and speed should be the difference, but what if this is the night where his skills diminish just enough to give Canelo the opportunity of a lifetime? That's one of the elements that makes this fight so intriguing. Still, the pick is Mayweather by decision, but it won't be easy.''
Constantino Viloria, El Diario, (Canelo): "Canelo is a great fighter, and has appeal. Mayweather has more experience. This is a very interesting - and even -- fight. Canelo can win if he can keep his speed and energy up to par.''
Otniel Batista, La Makina Deportiva, (Canelo): "Mayweather has shown he is the best pound for pound. This is Canelo's fight to make himself a millionaire. He's going to have to study Mayweather and his every detail, but I think Canelo can do it and will win. I think there will not only be 1 more, but 2 or 3 more fights between them."
Eduard Cauich, HOY Los Angeles (Mayweather) - "Mayweather will win by decision over Canelo, a 23-year old who has the potential for a huge upset, but it is unlikely to happen due to his lack of experience in a big scenario like the one. Mayweather will win a close fight but Alvarez will show that he can beat Mayweather in a couple of years as he gets better and Mayweather's career comes to an end."
Jorge Ebro, El Nuevo Herald (Mayweather) -- "I think Floyd is going to win -- not by KO, but by the volume of his combinations. Floyd hits more frequently and precisely than Canelo. Also, Alvarez's defense has too many holes and he will pay for this mistakes. I don't think that 'Money' has the power to erase Alvarez's anatomy, but the Mexican is not in the same class as Mayweather.''
Alan Massengale, RINGTV.COM columnist/blow by blow announcer, (Mayweather): "I would love to predict a Canelo victory, which always makes a pundit look like a genius when it happens. But until I see a drop off in Mayweather's ethereal speed and quickness, which hasn't happened yet, he wins by unanimous decision."
Felipe Valenzuela, CBS Sports Radio Houston, (Mayweather): "Canelo is more mature. He is focused and looks ready to be the best of the best. We have the biggest matchup in boxing in recent memory, two fighters with a combined record of 86-0-1. It would be marvelous for Mexican boxing if Canelo wins, but I think it will be difficult, 'Money' is a warrior and a great fighter. We just have to wait and witness this amazing fight on Sept. 14."
Norm Frauenheim, The Ring/www.15rounds.com, (Mayweather): "Canelo Alvarez will keep it close with a body assault that figures to target Mayweather's shoulder roll. But Mayweather's speed will turn him into a moving target never seen by Canelo and his punches will land with precision that the young Mexican lacks in a narrow win via decision that sets up a rematch.''
Mike Coppinger, USA Today, (Mayweather): "I've never picked against Mayweather and I won't until I see some -- any -- decline. Mayweather looked marvelous Robert Guerrero in May, and his combinations and footwork were as crisp as ever. I expect Canelo Alvarez to press the fight and work the body, winning a few rounds, but Mayweather will come out on top once again, winning a comfortable but close unanimous decision.''
Ken Miller, Los Angeles Sentinel, (Mayweather): "I believe that Floyd will out-counter Canelo for the early part of the fight and bust him to the body frequently, setting up the stage for a stoppage in the latter part of the fight. The weight will be huge, those two pounds and the courage of the Mexican will do him in. Floyd takes it by TKO 9.''
Grant Gordon, Glendale News-Press/Los Angeles Times Community News, (Mayweather): "Though Alvarez has improved with seemingly every fight and has proved he belongs on this stage, Mayweather is still Mayweather. 'Money's' defense and ring generalship will dictate the tempo and win the rounds and he'll survive a potential scare or two to win a clear unanimous decision.''
Miguel Angel Cebreros, ESPN Radio Spanish, (Mayweather): "My heart is with Canelo but my money is with Mayweather. There's only one fighter than can defeat Canelo in his weight class and that's Mayweather, who will win a decision.''
Ralph Gonzalez, The Sweet Science, (Mayweather): "Mayweather will be too fast, too crafty and too elusive for Canelo Alvarez and will win via unanimous decision.''
John DiSanto, PhillyBoxingHistory.com, (Mayweather): "Size and age advantages won't be enough for Canelo. He's good enough to put up a fight and may even give Mayweather a scare early on, but if Floyd is still Floyd, he will make the necessary adjustments and win a comfortable decision.''
Benny Henderson Jr. , Boxingtalk.com , (Mayweather): "Like him, love him or just plain look at him as an egotistical maniac, you cannot deny Mayweather's skills in the ring. Canelo is young and hungry, very aggressive and many would love to see him win. But, unless time has caught up with Floyd, I believe Mayweather will be too crafty, too fast and too experienced for the young lion. Mayweather wins a unanimous decision.''
Geno McGahee, RingsideReport.com, (Canelo): "The youth, strength and body work will be a test for the older Mayweather and I'm not sure that he can deal with it. Canelo, unless he gets completely frustrated, will wear down Floyd and find the mark late in the fight to win by TKO 10.''
Ramon Aranda, 3MoreRounds.com, (Mayweather): "While Alvarez is bigger, younger and stronger, Mayweather has yet to show signs of slowing down and continues to show why he is the best fighter in the world. I expect Alvarez to put immense pressure on Floyd early on until Mayweather establishes a rhythm and an appropriate distance. While a difficult fight, I see Mayweather pulling away in the last third of the fight en route to a hard-fought, unanimous decision win.''
Jerry Hoffman, ESPN Radio Central Coast, (Mayweather): "Floyd will control the pace, avoid big shots that will become flailing as the fight wears on and frustrate Canelo into making mistakes. Floyd will take advantage late and stop Canelo in 8. The bout will begin much like it did against Guerrero, but Mayweather will make Alvarez become brave and he will pay for it.''
William Trillo, Pound4Pound.com , (Mayweather): "Coming off his dominant performance over Guerrero in May, Floyd will be a finely tuned machine. Although Canelo did show signs of improved defense against Trout he will have too big of a challenge. Look for Mayweather to triumph by late round stoppage.''.
Giancarlo Oquendo, Puerto Rico Sports News, (Mayweather): "Canelo will earn the respect from the fans and the media and may even embarrass Floyd on two or three occasions, but Mayweather should otherwise dominate and win a unanimous decision.''