I have lived in and around Toronto for 40 years and have camped in and around Toronto for all of those years.
Camping - Closest I know of are on the West side of the city.
Bronte Creek Provincial Park, Oakville, ON Bronte Creek
Indian Line Campground, Brampton, Ontario Indian Line
Both are on or close to major roads into the city.
Traffic - Big City, lots of traffic. If you are not allowed to leave the TC in the campground parking will be a big issue. City lots are often multilevel or ground level and tight. There is a decent subway system and you could park the truck and TC at the end of the subway line and use it to get into the city. You could park the rig at the Yorkdale Shopping Mall and subway in from there.
Restaurants - too many to count and range runs from simple and cheap to luxury and expensive. Search the internet for listings and ratings.
Best time to visit - June, July, August, September. May is cooler and wetter, October is cooler but has great fall colours. July and August is school holiday time and busier since families take vacations then.
Toronto is a great and vibrant city. The CN Tower, Distillery District, Toronto Islands, walk the downtown park of Yonge St. for a start.
If you have time go down to Niagara Falls and spend a couple of days visiting the sites there. Riverside RV Park is 10 minutes drive South of the falls and a nice park to stop in.
Hope you enjoy your visit.
I had this company GM Roofing do work on my park model trailer including new cabinets. Their guy did a great job. I would not hesitate to get them in again for cabinets (or any other kind of work).
My park model is in Pharr, TX, not too far from Mission.