I've never been, but I've heard a lot of great things about Sandbanks. It's south of Belleville, though.
We love Sandbanks (pretty much the only place we camp in the summer - it's like being at the beach in Ontario) but it's nearly impossible to get lakeside (beachfront sites). Also lakeside sites do not have any hookups so they're not for everyone and it's a VERY busy park (unless you already have reservations, it's probably difficult to get mh sites for any weekend this summer (the vast majority of sites are booked within 10 minutes of being available in the 5 month reservation window)).
I suspect that most other provincial parks have some sites that are lakefront that are much easier to get and have hookups (We've gotten lakeside / lakeview sites at Sharbot Lake and Bon Echo without having to reserve much ahead of time - although this probably isn't really in the area the OP is looking for).
gokart2 beat me to it. I have stayed at North Shore RV Park a few times and it is nice and quiet. Not far from Trenton or Brighton run by a great family.
I have also stayed at Golden Beach Resort near Peterborough. It is on Rice Lake but, if I remember correctly, the non seasonal sites don't have a water view and it is a bigger campground therefor has a little more activity. It is also well run.
Enjoy your vacation and safe travels.
Life is partly what we make it, and partly what it is made by the friends we choose.