I'm Canadian and live in SW Ontario. I have travelled and camped both ways many times. If you're not sightseeing in Toronto, I would take the south route. Much more scenic and cheaper gas for a start.
The north side takes you through Toronto. The QEW and hwy401 are very busy and usually backed up with traffic, no matter what time of day or night. I avoid it as much as possible.
Darlington is not a nice park. Right in the city and right next to the highway. Sandbanks is nice and really popular. Never been to Ferris or Charleston so can't comment on those. Consider Presqu'ile PP if you go the North route.
The south side takes you by not only the parks you mention, but consider Letchworth SP, and Watkins Glen. The finger lakes area is beautiful, then Adirondacks etc. Much nicer IMHO.