I'd bet that Alvarez would be penalized much more severely than Floyd was in that case, and I'm not aware of anything which prevents such stipulations in the contract. There may be a set fine by the athletic commission, but the fighters are also free to determine what penalties for missing weight would be on top of that. Floyd had probably made sure that Marquez had no leverage on him for missing weight, and that the total opposite will be true for Alvarez in this fight. It was also Canelo who offered to make the fight at 152, Floyd did not ask for the catch weight, apparently.