Nacho berinstain is a great trainer, sure he would do great with him. Roberto garcĂa I think that did a good job with maidana and that would do a good job with canelo too. Basically any top trainer would do a wonderful job with canelo, he is the boxer every trainer dream about, and canelo would improve x1000000. Though, I understand canelo not leaving reinoso, and I respect that too. Edit: I respect that, but that's not the most intelligent thing to do. Though, sometimes winning or money is not everything. If it works for canelo, then it's fine, but I repeat that he would be 10000 times better with a proper training.
Roy jones or Manny Pacquiao from recent times. Pacman for example became fighter of the decade with limited skill. Can't cut of a ring. Doesn't know how to block. Doesn't know how to fight on inside. Never learned to counter punch. Still became fighter of the decade.
Prime Roy Jones easy. Floyd's up there of course. James Toney as well (too bad he was lazy). I'd actually put Calzaghe up there. Did what he did pretty much all off natural ability without brilliant technique.
I think Toney was very 'trained' but Nunn is a good choice because he was so smooth, loose and free-flowing and well-balanced and you can't really teach it.