Alcohol is actually permitted in Ontario Provincial Parks - the only restriction that may be in place is on glass bottles, but I think that varies by park. I wouldn't be worried about rangers confiscating the alcohol, although if you're planning on being loud then that's not nearly as tolerated (since there will be campsites all around you). Although as I type this, I realize that your concern probably stems from being underage - and I don't know how much they enforce that, since it never was a concern for me. So, yeah, take that however you see fit.
As for backcountry camping, I've had friends who went to The Massasauga Provincial Park just outside of Parry Sound and enjoyed it. The campsites there are water-access only (so you'll have to rent a canoe), and are quite secluded. This is considered an "operating" park, so the sites are maintained, and they'll have what's known as a "vault privy" as a toilet - basically a box with a toilet seat on it that goes into a hole in the ground (and usually isn't enclosed like an outhouse, either). It won't be right next to your campsite, though, so there's a little privacy there. Other provincial parks have backcountry sites as well, just take a look at
http://www.ontarioparks.com. Most of them are quite far north, though - Algonquin and Killarney are two of the big ones.
If you want true backcountry camping, you could either go the crown land route as you've mentioned, or go to a "non-operating" provincial park - this means that they are not staffed, and not as maintained as "operating" parks. I doubt that they have vault toilets at them, though, so most likely you'll have to dig :p
Anyway, hope that helped!
