I think that he is too old to go that much up in weight. His body would not be able to gain that much muscle without losing too much speed, which he needs as he is not a natural cruiser.
JC is at a stage in his career where he will likely only fight the big names for the big money. And there really are no "paydays" at cruiserweight. He will likely fight (winner of Taylor/Pavlik) or (winner of Jones/Trinidad). I just don't see him fighting a Chad Dawson or Tarver. I think what will be interesting when and if JC fights in America will be the "crowd" effect. 55,000 people shouting in his favor had to affect Kessler and it won't be anywhere near that in Vegas. Ideally, I think JC would get his best fight by a rejuvinated Roy Jones or Kelly Pavlik. I think Bernad is a lot like Evander, in that they look great (especially for their age) but the timing, reflexes and hunger are just not there...
Calzaghe has already offered Tarver a fight but Tarver priced himself out of the market, as he usually does. Neverthless, I agree that Pavlik is the best opportunity for a big money fight. Interest in the match will depend on how Pavlik looks against Taylor. From the point of view of styles, it would be a great match. Pavlik has the style that could prove to be very difficult for Calzaghe. Unlike Kessler, Pavlik spends more time coming forward and pumping straight punches at his opponent.