Squall would be played by Spoony, of the Spoony Experiment. Hands down, he'd be the best for the role.

Cid would be Robin Williams, you are spot on right there. Seifer would probably be Leonardo Dicaprio. Just a hunch though.

Zell would not be Brad Pitt. No, we'd need Mike Tyson to play Zell. I'm sure I don't have to explain why.

Rinoa would be... umm... Kristen Stewart. Just because.

Ultimecia would be played by Betty White, don't ya know?

Irvine could be John Travolta, this is a possibilty, but wouldn't High School Musical's, Zac Effron be much more suited for the role? Think on it.

Selphie, hands down, would be played by some Disney Channel chick. Just pick a random one, any one will do.

Quistis would be Megan Fox.

Edea... Hmm... I'm not sure.

You forgot Laguna! Now John Travolta could easily be Laguna. Consider that. Ward would be played by a random nobody and Kiros would be Eddy Murphy. Or Samuel Jackson to contrast with Travolta, if you know what I mean.