I've done northern Michigan a few ways, M23 along Lake Huron, M31 along Lake Michigan, or just blast up I-75 to get the most time in the UP.
There's the "Circle Lake Michigan" ride.
There's the Copper Harbor run.
There's Route 2 to Duluth.
If you all have passports, the circle around Lake Erie takes you through Ontario. Or the Trip to Toronto is great if you want to emphasize "eat" with the meet & greet!

There's some excellent routes, count me in.