I agree that Casperson could be our best bet, assuming that he’s interested in running again—he’s a lifelong Yooper who represented a portion of the UP in the state house for 8 years. The one downside is that he got trounced by Stupak in 2008, losing by 2:1.
I actually think Stupak would win re-election if he ran again. It would be closer than usual, but "Bart's a good guy and does his best" as they say up there. Everyone u there seems to call Stupak by his first name, much as I refer to Tim Walberg here by his first name. That explains his strength.