Chris and I took a drive earlier in the week and checked out these two parks close to Orillia. Both of them are small, with limited amenities, but we figured for a quick night away, they might be worth checking out.
Since both of these parks are pretty small, I'm just going to write a quick review of them...
Bass Lake is just west of Orillia, off highway 12. There is a small beach (easily accessed to day users) and a park store (was closed when we were there, obviously) which is close to the beach, so even if you're just there for the day you can probably get drinks or snacks, or sunscreen if you happened to forget yours.
The sites here are pretty much all woodland type sites, and range in quality from a rating 2 to a 4. (Keep in mind it's a bit hard to judge accurately when there's no leaves on the trees and still 2 feet of snow on the ground...) Also, if you plan to head to Bass lake, remember the entire outside of the park is bordered by small roads (there is a fence with barbed wire and stuff) so if you get a site on the edge, you'll hear cars going by. I doubt any of them would get a lot of traffic though, they seemed like cottage access roads.
Mara is pretty much 5 minutes down the highway from McRae Point and is a bit smaller than that park. We didn't have time to check out the beach, but the sites were more private, and were woodland sites compared to the more open sites at McRae. The outside sites back onto a cottage road, just like Bass Lake, but again, I'm doubtful there would be much traffic on them. The only thing that might bother you is that having cars driving by a few feet from your campsite would detract from your "wilderness experience" then again, camping 5 minutes outside of a city isn't likely to fool anyone into thinking they are getting a real wilderness experience.
In all, I'd say both parks would be good for a quick weekend away, where you don't want to travel too far because you only have a night or two. I think both have good fishing opportunities, so if you have a boat and are looking for a place to go where you can spend the day casting your line out, followed by a quiet night, both parks would be a good bet.