Ontario Parks is a great place to start. If you are in the area, try Grand River Conservation areas. They offer lovely camping. Brant has a great pool ~ zero depth entry. Elora has awesome scenery. Paris has trees and quiet. If you are in the GTA, Bronte is a great place. Close [Oakville] and pretty. You can use the zero depth pool too!
Hamilton Conservation area has nice parks too. We really enjoy Valens.
You can check out private camprounds by googling Ontario Private Campgrounds. They have a good search feature to narrow your park down.
We are in a permanent campground in Acton. It's very pretty and has a pool....a COLD pool, but it's a pool.
Niagara Falls offers nice parks, but they can be a little "trailer parky". KOA and Yogi Bears are good. King Waldorf is great if you are planning Marineland.
We've been to LOADS of parks in Ontario. We are the Tree-Hugging-Nature-Loving-Hippy-Dippy Family in Mississauga!
Blessings, Sandra