Toronto area campgrounds
The 2 major highways west of the GTA (Greater Toronto Area) are the 401 and the QEW. Milton is up near the 401.
If you are looking for something down around the QEW, Fifty Point Conservation Area has full hook ups.
Do be aware that traffic, as you get within 100k of Toronto, is horrible.. If you plan on exploring the city, I would agree with the transit recommendation. From Fifty Point, head to Burlington and catch the Go Train.
Carmen and the pack
2015 Coachmen Clipper 17BH
2017 Dodge Durango Citadel 5.7 Hemi