The City of Toronto runs two campgrounds. Indian Line Campground that is near Pearson International Airport and often filled with tradespeople working in the area. The other one is quite far out in the east end, Rouge Valley Campground that is not FHU. Very popular with the locals as well but a good hour or more outside the city centre.
Further east is Darlington Provincial Park where you can drive to the Oshawa GO train station and take the train into the city.
On the west side of Toronto is Milton Heights Campground, actually in Milton. We have been going there for years and about two years ago has new owners. The campground is exceptionally well kept and maintained and the front desk people very courteous and welcoming. Again you can take the GO train into Toronto.
A little further west from that is a KOA that I know nothing about other than it is a typical KOA.
There is also Bronte Creek Provincial Park in Oakville (west of Toronto) that is quite nice. We have been there frequently also. Go Train is also available from Oakville on a half hour basis.
Hope this helps.