CanaDream is the most popular RV rental outfit. Although, have a look at
OWASCO RV Rentals (on the east side of Toronto in Whitby) too - I've used them before and have been very happy with their service.
As most everyone has mentioned, you'll have a limited choice of campgrounds after the October 14th Thanksgiving holiday.
Down Picton way, the only campground that comes to mind and will be open after the 14th is
Rideau Acres (about 45 minutes further east in Kingston). Its a great park and the area is great for tourism. If you make it there before the 14th, head to Presquile Provincial Park - beautiful sunsets, great hiking and birdwatching.
Algonquin will be the highlight of your trip. The Mew Lake campground in Algonquin will be the only one open after the 14th. Its a great location for base camp for exploring the park. Make sure that you've loaded up with groceries and anything else you'll need before you go in the park, because the camp store will be closed and its at least a 2 hour round trip to town.
Over towards Collingwood, if you make it there before the 14th, head to Awenda Provincial Park. Its a beautiful place. If you get there after the 14th, Craigleith Provincial Park is open 'till the 27th. Craigleith doesn't really have the scenery, but its close to Collingwood and Owen Sound for doing the tourist thing.
If you carry on 90 minutes further south/west, MacGregor Point Provincial Park is open year-round. If you feel like travelling a couple hours a bit further south, the Pinery is also open year-round. Both MacGregor Point and the Pinery are well worth a visit.
Valens Conservation Area outside Cambridge is also a great park that's sort of on the way back to Toronto (and will be open after the 14th) and you'll be happy to spend a night or two there. Also, Milton Heights Campground in Milton (also open after the 14th) is out that way and is a clean private park close to the big-box shopping.
A couple of cautions:
- If you're camping on the weekend of October 11th-14th (including the Sunday night), you will need reservations. Everything will fill up for Thanksgiving weekend. Actually, most of the spots are reserved already, so don't leave this too long.
- After the 14th, water spigots will be turned off in most parks. You'll have to visit the comfort station (usually in the laundry room) to fill a container. I suggest that you just ask a camping neighbour if you can borrow their water jugs for a few minutes as opposed to buying one; this is Canada - virtually noone will hesitate to be of assistance.
