Rattlesnake is OK although there is some light logging in the area and when we have stayed, there has been a generator running all day and all night to power the accommodations for the workers. Watch for deadheads in the harbour. Our anchor rode wrapped a large deadhead two years ago. We were able to free it easily with a boathook.
I have never heard or seen any cruising information on the south side of Manitoulin. Richardsons shows there may be some spots. You may wish to sign up with the Great Lakes Cruising Club (some deals usually available at the Toronto Boat Show)... they have some info on a few harbours and anchorages but there isn't much between Providence bay and Great Duck Island / Burnt Island Harbour. Hopefully you can get better info before your trip. The North Side or Manitoulin (i.e. the North Channel) is about as good as it gets so, in my view, it's hard to spend precious time on what I suspect is a second rate cruising ground on the south side of the island. Even at the height of the season when it is busy around the Little Current / Baie Fine area, there are still great spots you can find and enjoy in solitude if that is your thing.
Georgian Bay, Ontario
Catalina 34 - "Good Idea"