It seems like a big fight, they say it's the next biggest fight after mayweather pacquaio, probably but by a long shot, it's no where near may-pac, I didn't feel the hype of this fight that much compared to may-pac.
I think because cotto defeated martinez, who had a bad knee, which I think martinez in his prime would have demolished cotto and then cotto faced delvin and geale at catch weights, this has made cotto's head big, as you correctly mentioned, that does not show me cotto has a chance against canelo, cotto is good, he had a good sparring session. He hit's hard, but a boxer who moves will give him problem, like austin trout, bad loss for cotto.
Canelo on the other hand, in my opinion, has been progressing nicely, especially the knockout of kirkland, his fight against mayweather was really bad, he just was slow, even though they were training him to be fast, so I don't think he will have speed but he does have the angles, like when he fought lopez, he was really good.
So this is a good match up, I think canelo will win, but not knockout, cotto does fall easy.
Canelo UD12
GGG is probably too big and won't come down and canelo won't move up, so canelo will have to vacate.