If I tell you anything I'd have to sink your boat if I see you on the water.
Lots of great places close by that you can camp out overnight. Each have varying amounts of other boats.
Ports is a great book and will give you years of exploring and places to anchor. Study it well over the winter and pick out a few spots to try.
Beausoliel Island is a National Park, you can anchor in many locations and have access to camping sites on shore with a user fee. Our favorite is Tonche Point mainly because our kids go to the YMCA camp that is right there. There are a few campsites, a picnic shelter and campfires. and always room to anchor. It's probably 1-2 hour sail from Midland.
Beckwith Island and Hope Island, are owned by the Beausoliel First Nation but are unoccupied. They allow you to camp on the beach with a user fee for the night. We generally pick the Island that is most protected from the overnight winds, either Hope, West or East side of Christian. If you don't watch the winds you will find out what the "Beckwith Bounce" is. The East side of Christian is the most popular and on the Sept. long weekend I lost count at over 100 boats and a very jammed beach. That however is unusual. The Sept. long weekend was awsome weather and calm so a lot of powerboats that normally would stay home were out, Thanksgiving weekend there were 5 sailboats on the East side, only us on the West side and maybe 5-6 sailboats at Hope. ( we stayed at each over the weekend). As flyingwleshman said it can be a 4-6 hour sail depending on where you go. The open stretch between Giants Tomb and Beckwith is open to Georgian Bay and can get nasty if there is a strong North wind, otherwise it is fairly protected and decent sailing.
Beyond that you can head up past Twelve Mile Bay to Massassauga Prov. Park which has several islands with campsites available for a user fee. You can get a map from the park office, I called and they mailed one out to me.
There is also some Crown land in this area that is a little harder to get into, but worth it and you can go ashore.
I have a map called French Severn Forest Land use ( mentioned in Ports) and is available at White Squall | Contact Us
It outlines all the public, provincial and crown land in this area. Also check this out Crown Land Use Policy Atlas
Beyond that, there is Killbear Prov. Park in Parry Sound that I've mentioned before. It can be busy, but has miles of beach, hiking trails, Interprative Centre and camping. It is 6-8 hours sailing in open water or protected channels inland.
One thing you will notice is the amount of boat traffic in the area compared to Toronto. The stretch up the west side of Beausoliel called the "Slot" can get very busy on the weekend and the powerboats can kick up a good wake. ( I describe trying to sail up through this area as trying to walk across the 401 and usually and up motoring until I get to more open water.)
Make sure you have a good chartplotter or study your charts well. There are lots of open water that has boat-biting rocks just below the surface.
Another great souce of info is this site, Sweetwater Crusing
, developed by a writer in Midland that has done articles for Sailing mags and has written a few books.
Hope Island Thanksgiving weekend
Beckwith West Thanksgiving weekend
East of Giants Tomb. If you look closely there are a red and green buoys close together to mark the channel, otherwise you're on the rocks.