For Detroit to Niagara Falls I'd stick to driving on the Canadian side it's a 4 hour drive. Highway 401 to Woodstock then take 403 right to Niagara Falls and exit at Lundy's Lane. Campark is a good choice but at the far end. You can drive around to the outlet mall and the tourist area. If you were to visit all Niagara Falls has to offer you'd spend a week. There's also wine tours and other things away from the falls. 2-3 days would probably be enough to move on.
Can't say much for Toronto in terms of camping. You might want to visit the CN tower, Toronto zoo, Toronto island or Eaton Center. For camping you might want to go either side or north. If you have a lot of time to spend you may want to go north a few hours past Barrie for a few days.
If you needed an in between campground between Detroit and Niagara Falls I'd recommend Pinehurst Lake near Cambridge. Small secluded conservation area with easy access back to the 403.
