I was also going to say the Halifax trip, but Barbie is right. The trip around the north shore of Lake Superior is wonderful. There are some wild and beautiful provincial parks, right on the lake, plus state parks in MN and WI. I took this trip 30+ years ago with my ex-husband and loved it. Here were some of the high points:
1) Believe it or not, Duluth is a neat city. I has a neat little historical restaurant called Grandma's right under the bridge where the river opens into the lake. Also, one of the best train museums I have ever been to. Duluth is a major shipping port for things like grain and iron ore.
2) Two Harbors is very scenic--woodsy with lots of cliffs and wonderful beaches overlooking the wild lake.
3) Thunder Bay was where the voyageurs left with their canoes full of furs for the east. There is a fort there and an Indian reservation. One of my most memorable experiences was attending a real Powwow with tribes from all of Canada and the U.S.
4) Neys Provincial Park on the north shore of Lake Superior. Bring everything because this place is very isolated, which is its charm. Right on the beach and gorgeous.
5) Sault St. Marie, Ontario and Michigan. Take a tour of the locks and watch the big boats go through.
Here is a circle tour site that will give you some information on places to see on the north shore of the lake:
http://www.lakesuperiorcircletour.info/I also like her idea of making a loop instead of backtracking. You could head east from here and go to Halifax, but we are really talking about a very slow 2-3 month summer trip. So what else do you have to be doing??