How close to Toronto do you need to be?
I've had this question before, and the short answer is there really isn't anything anywhere near the City of Toronto, big or small rig. There isn't much that I can think of in the GTA, unless you head north of the city towards Lake Simcoe. Or east towards Kingston/Trenton.
That said, Glen Rouge or Indian Line might work, but as far as I know, you have to get miles outside of the city to find anything like a commercial campground with FHU and concrete pads.
Milton Heights is also an option, but I would read the online reviews before committing. It sits right beside the 401 (very busy highway) and is near the glide path for Pearson Intl Airport, so be prepared for some 7X24 noise.
In my opinion, I would have to say Toronto is not RV friendly.
I haven't lived there for over a decade, so maybe a current area resident can help with more current information and opinions.
EDIT: Wife suggested a casino might work. Google "OLG casinos in the gta" to get a list of Ontario Casinos near Toronto. I'm not sure about their overnight parking policies, in general.
I know the one near us was just sold to a private group (Gateway Casinos and Entertainment, and will be renamed as a Starlight Casino), so it's no longer OLG, but it does have a fairly lenient and accommodating overnight parking policy, as long as you do a little commerce with them.
Mike. Comments are anecdotal or personal opinions, and worth what you paid for them.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)