I believe some units at Deerhurst Resort are fractionals, but they also have regular single week ownership as well (called Birchcliff Villas, RCI #1948). The parents of a co-worker of our DS bought 2 fixed weeks (last week of July, 1st week of Aug) in a 2 bedroom there when it first opened up many years ago & they paid a small fortune. They figured it was easier, & cheaper in the long run, than owning a cottage since they lived too far away to go up for weekends. I have no idea if there are resale weeks available. They offered the deed for the 2 weeks to our oldest DS for $25,000 last year!
There are quite a few private (non-timeshare related) fractionals in the Muskoka area as well.
~Diane