Ever since I was a kid and we'd camp at Algonac State Park I have been fascinated by the big ships sliding silently along the river. Sometimes I'll jump in the car and go to Algonac to try and catch a glimpse of some. It's kind of like train spotting, only I don't shoot heroine.
Avoid huge delays at Sarnia or Windsor by crossing into Canada on the ferry at Algonac (or Marine City). Average about 30 minutes waiting-and-crossing time, but then the dozen cars get waved through customs in a minute or two. No hassle, no traffic.
Several years ago the city of Algonac invested a good deal of money in creating a nice little board walk with benches. During the summer people fill the walk way to fish or watch the freighters. In the winter, the view of Canada is unobstructed.