Who can beat Floyd?

So, we all know that Floyd will likely have two fights in 2013 (or that's the rumor), and we obviously know that a boring, cherry picked fight with Timothy Bradley would make a lot of sense given Floyd's history of taking the fight he feels most comfortable with. These "two fights" will most likely be his last two, but, I ask, who...of his potential candidates can actually beat him? The rumor is that Floyd will once again fight on Cinco de Mayo, which leads to the question of which Mexican fighter does Floyd take? He basically has three choices, in Guerrero, Canelo Alvarez or a second fight with (a new, improved?) Marquez. After knocking out Pacquiao, I imagine the one fight that bothers Marquez is his 2009 washout against Floyd, where he climbed two weight classes, and fought the best welterweight in the universe, who happened to exceed the weight limit. Floyd has to feel pretty comfortable with the idea of facing the guy he dominated in 12 easy rounds a few years ago, and I'm positive that JMM wants another shot to prove himself. When JMM has a vendetta, and an idea of revenge, he goes for it, so I imagine Marquez/Mayweather 2 as a fairly possible option in 2013. I'm not sure if this possibly stronger, more confident Marquez can give Floyd the fight we'd want to see, but it's in the cards. As far as the casual fan is concerned, Marquez is the biggest name RIGHT NOW, and Floyd will want the money. The Ghost Guerrero can bang. He's young, he's likely in his prime, and he wants the best. He deserves the best. I think he has a good shot at beating the best. A fully loaded, smart banger, who will test Mayweather, and force a real fight. Beating Berto was enough for Ortiz to earn his shot against Floyd, so why not the Ghost? Floyd does well against aggression, so why not give Guerrero a chance, given his youth, and the fact that he's no ordinary banger? It's Floyd's best bet at proving he's not a cherry picker, and that he's not afraid to go toe to toe. Canelo is the future of boxing. Oscar is trying to preserve him, and keep him away from anything too risky, since he's only 22, and as he gets older...he'll become the premier showcase PPV fighter. Why possibly ruin that with an early match against the best boxer alive? Because he presents the biggest threat to Floyd's crown. If an aging, almost-done Cotto can pressure Floyd effectively, bloody his face, and actually steal consecutive rounds, then imagine what the youth, energy and power of Canelo will do with Floyd? This possibly presents the best fight Floyd Mayweather has had in years. Bradley, Marquez, Guerrero, & Canelo Alvarez are the four options. Bradley's the one I dread, because it's the easy way out (stylistically), in my opinion. Marquez is the one Mayweather would be the most comfortable with, and would likely make the most money right now. Guerrero is the mandatory challenger for the WBC belt, and I think presents the most intriguing war. Canelo is the fight that likely scares Mayweather the most.