Check out the Toronto Regional Conservation Area campgrounds. There is a website and you can reserve online. We stayed at the Indian River Campground last week with full hookups. It is fairly noisy, being between 2 Highways (407 and 427)plus a rail line right beside, but it does have transit! There are 1 or 2 stops that are Brampton transit, and then switch to TTC. Did not need, as we have a TV and TT so just unhook and go, but I saw the stops. There is also Rouge Valley, but not sure about transit. Can't think of any boondocking sites that you would not get hassled, unless Walmarts. There are also campgrounds up North of the 404, but you need a car. Lived in TO for 40 years and escaped to the country in 2008.
Tina & Ted & pooches
2012 Ford F-150 XLT 5.0L V8 4x4 with tow package
Andersen WD hitch with sway prevention
2012 Rockwood UltraLite 2304s trailer