Obviously Mayweather would whoop him. They won't fight. Have two Al Haymon fighters ever fought each other? (legit question) Berto has just come back from a loss, Al Haymon is all about maximising a fighter's potential to earn money, he won't let another sure loss happen.
Al Haymon isn't going to let Floyd Mayweather and Andre Berto fight because its conflict of interest. Unless the fight was an absolute, unavoidable, option, but if they can get the Pacqauio fight I'm sure they'd take that instead of Berto. Floyd Mayweather would handle Andre Berto pretty easy, but I don't think he'd knock him out. Chances are he dominates Berto for 12 rounds leaving the crowd unsatisfied.
What part of "Berto has just come back from a loss" are you not getting? He lost to Ortiz, recently came back against Zaveck. Now that he's got another title, they will milk it just the same as they were doing before the loss, which really was a cherry pick gone wrong vs Ortiz. Haymon is not putting him in with Floyd to suffer his second loss in three fights. Floyd makes Haymon money with or without Berto