Luke, Leia, Han, Lando, Chewebacca, and the droids would obviously have to be played by the original actors. If there were to be force spirits, Ewan McGregor and Hayden Christensen would have to replace Alec Guinnes and Sebastian Shaw. Liam Neeson and Frank Oz could reuturn as Qui-Gon and Yoda if necessary.
As for the rest of the cast:
Mara Jade: Dina Meyer
Jacen Solo: Sean Patrick Flannery (Nice choice!)
Jaina Solo: Claire Danes
Anakin Solo: Jake Lloyd (If he can act as a young adult, sure.)
And just because I think they'd be perfect in the roles:
Grand Admiral Thrawn: Jeremy Irons
Joruus C'Boath: Donald Sutherland