We have done most of it in pieces. Two campgrounds come to mind that we really enjoyed. Association Island (now a KOA) in Henderson New York, was really great since you were on an island in Lake Ontario. For different reasons we also loved the Hattie Cove Campground in Pukaskwa National Park in Ontario Canada, which only has a few big rig 30AMP electric campsites. It was a true wilderness experience on Lake Superior.

I've never done this trip but I can suggest (not necessarily recommend) a couple of campgrounds around Detroit since the camping is fairly sparse. The first is the Wayne County Fair Grounds in Belleville it's not terribly well known and is probably the closest to downtown. The other is Sterling State Park in Monroe which is about an hour from Downtown but it is on Lake Erie. As for other camping, Michigan has lots of campgrounds in National Parks and Forests, State Parks and Forests. The state forests are probably the least used but you'll have to boondock as most only have vault toilets and a hand pump for water, but they are cheap. As for the state parks if you're here from Memorial Day to Labor Day they can be booked up especially on the weekends. As for stuff to do around Detroit I wouldn't miss the Henry Ford Museum and Greenfield Village, they are world class. Also don't sell the "sunrise side" (east side) of the state short. If you're into ship watching Port Huron has a park on the St. Clair River which is perfect for such activities. Someone publishes a guide as to when particular ships are passing if you have an interest in a particular ship. Once you cross the bridge (the Mackinac) you're into copper country and there is lots of history. The Soo locks are also pretty interesting. If you go to Canada, and it looks like you will, you will need a passport or an enhanced driver's license to get back in the US. If you do any fishing and have fish in your coach I would check with customs before you go into Canada, also if you want to bring fish out. I believe you have to leave one sq. in. of skin on each filet so they can tell what kind of fish you have. Not completely up to snuff on it but I know it can be a big issue at times. No fish no problem. I imagine other game meat is the same just so you're aware. As to fishing in Michigan there are world class trout streams but don't overlook the toothy critters like pike, musky and for really good eating walleye. If you want to go musky fishing Lake St. Clair is one of the best musky lakes in the world but you will need a Canadian Fishing License. The only only other suggestion I have is to go around Chicago if you don't care to see the lakefront. You can't make it around it without paying some tolls but if you don't go through downtown you can save some money. I believe there is a state park in Indiana on Lake Michigan which is probably the closest to Chicago, but check it out for yourself as I'm not too familiar with that area. I imagine you are going to go to Niagara Falls. If you do the views from the Canadian side are better than from the US side. The maid of the mist tour is worth it. Not too long and you will get wet but it's a once-in-a-lifetime thing. Have fun.

Things not to miss around Michigan:

Meijer Gardens in Grand Rapids
Sleeping Bear Dunes National Lakeshore
Traverse City
Petoskey
Crossing the Mighty Mac bridge (between upper and lower peninsulas,
Stay at Straits State Park campground and then take ferry over to Mackinac Island and have some fudge! No cars allowed on the island.
Sault Sainte Marie, do the boat trip through the locks
Tahquamenon Falls in the Upper Peninsula (UP - you become a Yooper being up there). Nice state park located there.
Picture Rocks National Lakeshore (take one of the boat rides)