Ok, here are my thoughts...
Cable - Michael Biehn
Eh, maybe. Gerard Butler would be better.
Domino - Mary Elizabeth Winstead
Um, too young. This is someone likely to be hooking up with Cable. Their relationship can't be father/daughter, which is what Winstead would be. Olivia Wilde would be better.
Psylocke - Elizabeth Tan
Eh, not sure if she has enough background. What has she been in? It's all TV series and shorts. I think Maggie Q is better, and I'm sure she can fake the accent if needed.
Selene - Monica Belucci
She is too old. Sorry, but it's true.