Pretty much see everthing!
Pictured Rocks is great, if you have time, Mosquito Beach is a good place to do some snorkling. Boat trip is ok, but kinda long, and not very hands on.
Plenty of waterfalls to see, most are easily reached from the car with a short hike.
If you have never been to Mackinaw island it's a fun day trip, if you like riding bikes, rent a bike and ride around the island, great time and very relaxing, you don't have to be in super shape.
Copper harbor is a great camp site, very close to water, northern lights, bears very cool rocky beach, lighthouse within walking distance
When in Marquette take a drive and do a picnic on Presque Isle, nice swiming/rock diving, deer, (one albino if still alive) very nice spot.
Porcupine Mtns. If you like hiking, hike to lake of the clouds, very cool, and great views
If you plan on looping through WI, definately plan a stop in Bayfield WI, awesome town, canoeing to apostle islands, great campsite just west of town on the water.
Ferg