One non negotiable: he must be able to do a proper Scottish accent. I will admit that I'd MOST prefer a Scot to have the role - but just LOOK at this guy! He IS Jamie Fraser. I am dying for Diana Gabaldon's opinion.
Let's see some Jamieisms, shall we?
"What have you done, Sassenach?"
"Dinna try me too hard, Sassenach."
"Ye're fools, the lot of you."