No apostrophe needed.
Josh Holloway from LOST would be my choice for Gambit, btw.
Meryl Streep also did "Defending Your Life," the comedy/romance/fantasy set in the Afterlife way-station. She seems pretty down to earth (no pun intended), so I doubt she sees any role as "beneath her." Hell, if she can do a musical full of ABBA songs, she can probably stomach anything.
Colin Firth has done some fantasy--"Dorian Gray" and "Nanny McPhee"--but I wouldn't mind seeing him in more scifi types of roles. He can fit into just about anything.
Mcconaughey, of course, was in "Reign of Fire." I can see him in other scifi/apocalyptic-type movies.
Bradley Cooper would be good, too. I can see him in a scifi film easily. He's apparently been trying for some time to get Dan Simmons's "Hyperion" made into a movie