Calling Scott and FB

Taking a jet catamaran to Mackinac Island is high on my list. Back on land, cross the incredible Mackinac Bridge and it's only about 90 miles north to Whitefish Point, which has a really nice maritime museum featuring artifacts from the Edmund Fitzgerald. Drive back south across the bridge to Mackinaw City and you're only an hour from Petoskey. I can't remember what I liked there, but it's a really neat area. Then you go another hour and a half south to Traverse City, Cherry Capital of Michigan. As I recall both Petoskey and Traverse City are full of incredibly beautiful Victorian-era homes.

Since you only have a few days, and you want to explore quite a bit of Lake St. Clair, you might want to focus mostly on the Detroit-area. For sure you want to see the Henry Ford Museum and Greenfield Village. It's been 30 years since I visited, but I remember it as being pretty incredible, with so much more than just car and manufacturing stuff. Since y'all are the right age, the Motown Museum is only about 20 minutes away.

Because our summers are so short, folks crowd a lot into the period between Memorial Day and Labor Day. Any tourist destination will be busy.

As KYF said, Mackinaw Island is a tourist destination. Plan on walking a lot as there are no cars on the island. In June it will be busy as the other tourists will be there as well. If you need T-shirts, Mackinaw Island is the place to go. Take the ferry ride from the north side of the Mackinac Bridge at St.Ignace. It is a shorter trip over the water. Bring a jacket as the air temp over the water will still be cold.
On the south side of the bridge is Mackinaw City and Fort Michlamilimac. The Fort is worth a visit for the history. There is the Old Straits Lighthouse immediately to the east of the fort and also worth a visit.

If you wish to venture further north of the Mackinaw Bridge & see some wilderness, the area around Tahquamenon Falls is beautiful. A bit west of the there is Grand Marais is a nice town on Lake Superior that is more geared for restful adult tourism.

Soo Saint Marie is home to the Soo Locks between Lake Superior & Lake Huron. There is a freighter ship museum to see on the east end of town. That town is also tourist oriented. Good food at the casino there.