Pukaskwa NP has a great campground (NE corner of the lake), beaches and hikes. Lake Superior PP (eastern end) has great hikes, one (Orphan Lake Trail) goes out to a really nice rocky beach, and also good backcountry kayaking and camping. We also like Pancake Bay PP, but only if getting a waterfront site. Sleeping Giant PP isn't quite a nice camping, but is still worth stopping at. If you have kids, the Amethyst Mine near there is a fun stop. We didn't stay in Thunder Bay proper - just drove in for the day when we were there. There's an old Voyageur re-enactment fort NW of town (can't remember the name now) that's also a fun stop. (There's also a private farm selling homemade Gouda cheese run by a Dutch couple - couldn't tell you where that is though. Good cheese.)
If going in the summer season, make reservations for the PPs early so that you can get a waterfront site. Pukaskwa doesn't take reservations, but we've never had trouble getting a site. (I like the sites closest to the beach there.)
Description of the drive along the Eastern shore of Lake Superior: It's like the California coast, but without all the people. Truly spectacularly beautiful drive.
