Interesting that PPP is expecting Walker to be the nominee- he is the only one ever tested against non-Clinton Democrats. But, this poll definitely suggests that Michigan could be in play (keep in mind that GOP numbers will improve when there is a candidate).
Don't be so sure. Republicans have nobody who has a strong appeal to Michigan.
The state has too many blacks and union members to be easy picking for a Republican. The last time that the Republicans won Michigan in a close election was 1976 -- with Gerald Ford.