Take the lakeshore trail along lake Erie in Ontario, very nice cycling. The Welland Canal is nice if you are into large ships, bridges and docks (has bike path along). Niagara region has lots of wineries. The Falls are a perfect tourist trap, but if you haven't seen the falls yet, I guess there's a checkbox waiting. The Canadian side is nicer. Point Pelee is also a Wine region, by the way. There's a few beaches along the lake shore.
Toronto is very busy and very urban. If you are into that, then a detour to Toronto might be nice, but if you are into the loneliness aspect of cycle touring - see if you can find more interesting things on your route without that detour.