Friends just returned from Isle Royale and really enjoyed it. Not sure you are planning to travel that far north and west.
We were in the UP in the beginning of June, and there was still ice on Lake Superior!
If you've never been there, Bronner's Christmas store in Frankenmuth is worth a short stop. I have friends who would go there every year, but once was enough for me. Glad I did it, but don't need to return.