I was one of those saying Morales would beat Maidana - if it wasn't for the eye which came from showing too much respect in the early stages then he would have and I'm 100% sure Morales wins by KO in a rematch. Maidana is a B level fighter.
A fight versus JMM would be a completely different prospect. Marquez is an elite level fighter, has a good arsenal and would not make the same mistakes Maidana did, both offensively where he didn't take advantage of the few opportunities he had to really hurt Morales, and defensively where he was wide open for El Terrible to score consistently throughout the fight. Whilst it was a good performance from Morales you really have to see Maidana for what he is before heaping too much praise on him - a close loss to an overrated statue, with little boxing ability but a fairly strong punch, does not mean you're ready to fight at the very top.
The only wildcard is the weight - one of the things we've learnt is that JMM doesn't carry the added bulk as well as some fighters do when moving up. If the fight takes place at 140 then it obviously plays in Morales' favour, but I still don't think it's enough of a handicap to prevent a Marquez win. If I was Marquez I'd favour a Maidana fight - he lacks that x factor that could cause an upset and it seems less of a risk. Morales is still returning to form, you can see from his physique that there's room for improvement, and the truth is Juan will box chino's face off for a good pay day, and Morales will be there for his next fight if he doesn't get that shot at Pac.
After that maidana fight this potential match-up definitely got a lot more interesting to me. I would have to give Morales a decent chance here, especially if the fight is at 140.