Pacquiao will land a lot more blows than Margarito or Cotto did. It all depends on how defensive Clottey is, but if Clottey tries to fight back every round he's going down.
I think he can but I think a decision win is more likely. There's an opening for Pacquiao's left hand straight/hook that he likes to use, the one where he throws a lazy right jab to get his opponents to open up, takes a step back and let's his left hand go, the one that knocked out Hatton and hurt Marquez is there against Clottey when Clottey switches from defense to offense, especially when he jumps when he throws his punches. Pacquiao is fast enough to take advantage of it and I'm sure he'll land it, what happens when he lands it, I have no idea.
I think it'd be a hell of an accomplishment. He'd have to wear him down and do it late, I'm thinking. I'm just Hoping he doesn't break his hands on Clottey.