Just you wait and see.
I have some old X-Men cards, that are of paintings of the characters. You probably remember them. Anyway, the cards for Jubilee and Shadowcat look almost exactly like Faruzia and Shannen Doherty, respectively.
Dolph Lundgren is washed up, and was never really worth anyone's time of day to begin with. At least the guy from Son of the Beach has the look and accent. If you can think of anyone else better suited, say so. But don't insult the X-Men movies with Dolph.
I think I could forgive the movies if they shrink Juggernaut down to giant size, but not ridiculously large like he is in the comics. And for that, I think Big Show or MCD would be good (considering they don't beat him, unmask him, etc).
Ethan plays Willam Black in Mallrats and in Chasing Amy. He was also in Evolution, and in American History X. He's a massive tub. Maybe some camera tricks could be used to make him look taller though.
As for Marsters, I always get his name confused for Marsden. So I figure why not have him play Cyclops' brother? Seems only fair.