Man, I did that years ago. Started in Duluth, MN headed over the top then back through the U.P. of Michigan.
In the U.P. , from Sault St Marie to Pictured Rocks area, on 28(?), is booorrrrring. I had to make some time so I didn't try the W. Lakeshore Dr. to 123 - 58 (I think). Other than that, following the roads along the lake was awesome. Couple of funky construction zones on the north side. I didn't find any real "twisties" but definitely scenic, non-slab roads. A really cool ride.
Things to see?
The locks at the Sault
Aerostich in Duluth
Floating Bridge in Ishpeming, or just east of it? Thats lower U.P. if you go there.
Iron Mountain, MI
Take 41 up past Marquette, past Houghton to the tip there.
Oh yeah, already mentioned, Pictured Rocks by Munising.