Jubilee could be just about any teenage girl that can act. Hit Girl probably would have been a fine choice if we didn't already associate her that way. If I were making a superhero movie though, it probably wouldn't involve Jubilee in any way unless it revolved around her 18th birthday orgy.
Gambit is easy. Turn on any gay porn, and the guy on the bottom would be just fine as Gambit. I was going to say Kuriin, but honestly Kuriin is far too manly to be Gambit.