If you have 3-4 weeks for this, at 50 miles per day that would be 1,050 to 1400 miles. It's hard to figure out a route not knowing just a little of what your capable of. Also, if your looking at transportation, that will make a big difference.
Another thing you may want to figure out is, do you want to see something different. If you go up to MN, well, most of the state looks like Iowa, Illinois or any other farming area. I don't mind riding in areas like that. The northern border of MN does not look like the southern border. The trees up north are a lot like the ones you see out in Colorado, spruce, aspen, etc.
If you have never been to Minneapolis and enjoy being in the city, I would spend some time riding around the vast trail system they have. Maybe visit downtown. Maybe get a hotel for a couple days to do this.
I'm not trying to steer your trip into MN, I've been there a few times with my bike; I trucked it up from MO just to ride some trails. I've never been to Michigan or Wisconsin. I bet they are nice.
You know this song?
https://en.wikipedia.org/wiki/The_Wr...und_Fitzgerald
I've always wanted to go here in Detroit:
https://en.wikipedia.org/wiki/Mariners%27_Church