Floyd, by stoppage if he can be arsed. Even hypothesising that Canelo makes the most out of his style against Floyd, Mayweather is too sharp and too smart for him, and apart from flurries(because he's a calculated fighter) does everything better and would break his man down. Canelo is not better at getting in and out, doesn't have anywhere near a good enough jab to throw off Floyds, and doesn't have the power to substantially damage or dissuade Floyd if he does get anything off.
Floyd would KO him at this stage. Alvarez is still very green for a world champion and has never boxed anyone near elite level. He is a talented kid who has a lot of potential and could be a future star if nurtured right, just keep him away from Mayweather or Pacquaio for the time being. If I were his promoter next year I would go for the following three fights (assuming he beats Cintron of course): JCC Jnr - get the year off with a massive Mexican showdown with JCC Jnr, I would fancy him to win this and I think they could have a good fight. Wolak/Rodriguez winner - another match he should win but would be a solid fight, I think he looks good against either. Kirkland (if he continues to win) - would be a solid match to cap off a good year, a win would set him up for big fights in 2013 were-by he can start to really move up to elite level.
Right now, Floyd would school him. There's really no rush with Canelo, they've put him under an unneccesary microscrope by giving him a strap. But he has all the time in the world.
I don't know why, but I have a feeling that Mayweather is going to fight Khan, Alvarez and Manny in 2012. He's been bringing up how he's going to fight a lot more in 2012 and how he's going to be the most paid athlete next year. All three fights are arguably the biggest fights out there for him. He'd beat 'em all, in my op.
^^^ If he fights those three next year then surely noone can have any complaints about Floyd. Bar a Martinez fight at 154 he's done all he can do really.