I toured around Lake Ontario last year and live in Lewiston, NY.
I would not recommend staying in the US to Niagara Falls due to the roads between the Peace Bridge and the Rainbow Bridge.
I would take the UGRR or the Northern Tier route across the Peace Bridge then take Follow the Niagara River North. Most of this route has a nice multi-use path except for right near Niagara Falls. Follow the river north through Niagara on the Lake. There is a waterfront trail, on and off road, that takes you around to Toronto. After St Cathrines, Ontario, Follow the North Service Rd and stay near the lake. There is a trail on the lakefront from Hamilton to Toronto. There is a bridge next to the QEW in Hamilton that is very hard to see on the maps. The route on the North Service Rd is very light traffic.
If you are camping I would recomend the Jordan Valley Campground. It is west of St Cathrines. Approach from the West.
Past Hamilton, in Oakville, there is Bronte Creek Provincial Park. Do not go to the main entrance, the campground entrance is on the East side of the park! About a 7+ mile detour with Heavy traffic:(. These stops seem to be about the distance apart as your existing plan.