Originally Posted by Pladio
I think another potential pick, which may sound strange at first could be Hugh Jackman.
I know he's mostly famous for X-Men but he has played several other roles that demonstrate a range of possible acting profiles. He already has the bulk of a Witcher and I think simply needs the white hair and scars (which is easy enough to do). He doesn't have a standard American accent either which can add some character like Mikkelsen.