The obvious analysis is the age old "good big man beats a great smaller man". Not big on cliches, but this one works for me. Miguel Cotto not being a very big welter, I don't see 145 as an issue.
As far as the matchup goes, I really like Cotto's ability to fight from a left handed stance. I think that takes away a lot of what Manny Pacquiao does from a "hit without getting hit" perspective.
Lastly, the theory that Manny will simply one punch KO Cotto early just doesn't add up for me. He's really only done that to one guy that we'd consider elite. Calling Ricky Hatton elite is a bit of a stretch too. Even in that case, it took a number of clean shots to get Ricky into one punch KO territory. Guys like Marquez and Larios withstood Manny's power, both having been hurt badly by lesser, smaller guys. Figure Cotto can too.
Going out on a limb with an odd prediction. My Prediction, Miguel Cotto 116-112. Both get buzzed, neither goes down. Manny goes into a bit of a shell late as body work piles up. Manny Pacquiao -v- Erik Morales I, revisited minus the butt cut.
This Saturday, tune your TV sets to HBO Pay Per view and watch the live broadcast of Manny Pacquiao vs Miguel Cotto. Check your local cable provider or satellite dish receiver for more information, including purchase price of the PPV and start times in your region.