Monsters Inc. because it is Disney/PIXAR. I know that it isn't being directed by the great John Lasseater but it looks to be pretty good with the voice talents of John Goodman and the funny Billy Crystal.
As much as I would love Monsters, Inc to do better, I think Harry Potter will be bigger. I'm sure Monsters, Inc. will be at number 1 for the first 2 weeks, but once Harry Potter comes out, I bet it will drop to #2. But I could be wrong and Monsters, Inc could blow harry right out of the water, wouldn't that be sweet?