As this summer's ride was my second time going across the continent from British Columbia, I actually took the south shore of Superior route through Michigan's Upper Peninsula. Most of the roads are better, but in some stretches along M-28 not much better. The terrain is flatter but goes through mostly monotonous forested interior with rare views of the lake.
The cycling advocates in Sault Ste. Marie have mapped out this alternative route that avoids much of Highway 17 east of the city. I tried it for a abut 60 kms but reverted back to the highway when one part turned into a really rough road and I didn't find my way back on to it.