Margarito will get completely dismantled. His pressure won't mean jack because he's too slow and his defense is close to non existent. Just look at the Cotto and Mosley fights. In the Cotto fight he won but took a lot of punishment and Cotto was hitting him at will coming in. Mosley was also hitting him clean at will. Against both fighters, he was just walking in not defending his face at all and just trying to bully them. Margarito's style of taking his opponents' best punches and outlasting them is a very stupid way a fighting if you want to have longevity in boxing, and I think all that punishment taken has finished Margarito. Someone that gets hit as much as Margarito doesn't stand a good change at beating Pac. Pac's movement and speed will have Margarito confused, and Pac's power will have him dazed by the 7-8th rounds. I doubt Margarito can even land any good punches on Pacquiao, but will get countered to death.
Manny SHOULD KO him within the first 5 rounds. Taking on Margarito, as far as I'm concerned, is like taking on an unranked 154 pounder, or a blown up and still unranked 147 pounder. Oh shoot, that's right this fight is at 151 pounds...