Dude.You could always hit Yankee Springs on the way up to Copper Harbor.
Yankee Springs is the first "destination" mountain bike trip I ever did. When I lived in IN, we'd heard about those trails so we got a small crew together and went up and camped and rode for a weekend. I consider it the first "real" mountain biking I ever did, to be honest. If I were to do a Great Lakes/Midwest riding focused road trip, I would totally want to hit all the trails I cut my teeth on as well as all the new school kickass stuff. Yankee Springs, Fort Custer, Pinckney, maybe do some riding around Traverse City. And then yeah also Marquette and Copper Harbor and all that nonsense.