The lasting images left from their first fight were Cotto being battered and retreating for the latter half of the fight. Selling the legitimacy of a second fight to casuals would be no easy task.
Cotto should fight Canelo. Period. Thats the fight that makes sense. Canelo has a big fan base, so does Cotto. Cotto is still close enough to his prime to be competitive. Who really wants to see rematches of Cotto vs Pacquiao or Cotto vs Mayweather when Cotto (although competitive) clearly lost both fights? If Cotto loses, to Canelo he should fight a guy like Cintron who has a name and doesn't pose a real threat and go on to retirement a winner.