23-year-old Anton Yelchin is a tad young, but with a bit of bulking up he'd make a fine Jedi. He's also a bit of a veteran when it comes to taking over iconic roles -- Kyle Reese in Terminator Salvation, Pavel Chekov in J.J. Abram's Star Trek. He knows what he would need to bring to the table in order to make the character his own, while still remaining faithful to what has been done before.
We've previously toyed with the idea of 28-year-old Garrett Hedlund taking over the role of Han Solo in some kind of prequel film. He's proven that he can give a grounded performance in an effects heavy sci-fi film (Tron Legacy) while maintaining just the kind of swagger and likability that made Han Solo the galactic scum bag that you can't help but love.
Alternate Choices: Nathan Fillion, Chris Pine.
I haven't built the strongest case for 24-year-old Mae Whitman as Luke's twin sister Leia. Going purely on resemblance to Fisher, she has everyone else beat. But she probably wouldn't fair well as a believable love interest for Han Solo. When she's not stealing scenes on NBC's Parenthood, she's been repeatedly cast as the ex-girlfriend before or in the way of the main love interest -- Arrested Development, Scott Pilgrim vs The World, Perks of Being a Wallflower.
Alternate Choice: Anne Hathaway
35-year-old Chiwetel Ejiofor is by far one of the finest actors working today. He could probably do an uncanny take on Lando in his sleep! His work as the menacing villain in Serenity and the flamboyant screw-up in American Gangster makes him perfectly believable as the kind of person who would pal around with as equally as shady and magnetic of a character like Han Solo.
Alternate Choice: Will Smith