Just curious, but why?
I'm looking at this as Mayweather would be facing a faster/stronger offensive fighter. Mayweather doesn't have big punching power, he's the best defensive fighter in the world, but mostly he avoids getting hit and tries to outpoint his opponent. I mean Mayweather hasn't had a true KO in well over a decade, he generally depends on decisions and I can't imagine him being able to outpoint Manny. There is absolutely no chance Mayweather scores a KO on Manny, so let's assume it goes 12 rounds, how would the score look?
Well they use four basic criteria.
1 - Clean Punching: Advantage Manny, though not by a huge margin.
2 - Effective Aggressiveness : Advantage Manny, this isn't even remotely close.
3 - Ring Generalship: Manny again, because of his aggressive style and speed he'll dictate the pace of the fight.
4 - Defense: Mayweather, you have to give him this, widely considered one of the best defensive fighters of all time.
So, odds are Manny outpoints Mayweather, and there is more of a chance Manny KOs Mayweather than the reverse. I'm not saying it would be lopsided at all, it'll be a great fight, but I'd feel rather safe that the vegas odds are going to favor a Pacquiao victory, as well they should.