Well, knowing that I don't have to limit myself to realistic choices, my choices would be ...

Eric Stoltz as Luke

John Saxon as Han

Jennifer Connelly as Leia

Christopher Lee as Tarkin

Michael Ironside as Darth Vader

Clint Eastwood as Boba Fett

Alanis Morissette with pasty white makeup and yellow contact lenses as Palpatine (she's done some acting, so this totally counts!)

Clive Revill as the voice of Palpatine

Vincent Price as Bib Fortuna

Gillian Anderson as Mon Mothma

Kenneth Branagh as (young) Obi-Wan

Heather Langenkamp as Mother Skywalker (I will not refer to her as Padmé!)

Kyle MacLachlan as Anakin

Conrad Veidt as Dooku.