I know that you can book nights at the Club Intrawest Blue Mountain Resort. The minimum for the booking is one night. If you're book 5 nights or less, you can book 7-days to 4-months in advance. If you're booking 6 nights or more, you can book 7-days to 7-months in advance. A non-refundable $95 booking fee applies.
I know that through II you can book at a Muskoka resort, but I really don't know any additional information on this.