Hopefully the story will be such that no recasting is needed. IF they did recast, I would hope that it was a straight up reboot (like Star Trek). I have no issue with a reboot, but recasting AND calling it a sequel...meh

That being said, I think Christoph Waltz would make a boss Obi Wan. Very different take on the role but I think that would be necessary to distinguish a new series from an old one (but since no one has mentioned a reboot, moving on)

Hemsworth or Gosling as Han Solo

Same people for C3PO and Chewbacca

Luke and Leia...no idea honestly...