I live in Sault Ste Marie, Ontario – north and west of where you will be, but I can offer some suggestions.
1. Buckwallow at Gravenhurst (northeast of Barrie). Well developed trail system with trails from easy to extreme (trials type riding). The terrain here is the Canadian shield with low rolling hills made of granite. ($10/day to ride)
2. Torrance Barrens (east of Bala). Rode here for the first time on Saturday. The barrens are Canadian shield granite ridges and the trail runs along these bare ridges – kind of like riding undulating pavement. (no charge)
This video shows footage of the trails at Buckwallow and Torrance Barrens:
http://www.youtube.com/watch?v=b0hjDhLaHrw&feature=plcp
This shop has links/info on Muskoka area riding:
http://www.ecclestonecycle.com/ride_mus … untain.htm
3. Hardwood Hills (Barrie) – I haven’t biked here but friends have and rave about the well marked and designed trails. (fee to ride) (http://www.hardwoodhills.ca/index.php?o … &Itemid=83)
4. Copeland Forest (Barrie) – Large public forest area with lots of trails. I don’t know if there are maps available, so if you have a gps (I use my phone) it can be helpful to find your way back to your car. Lots of variety of trails – some flat and easy, some steep downhills with switchbacks.
5. Don Valley Trails (Toronto, downtown) – read lots about them, but have never biked them. I think there are groups with regular rides here.
6. North Bay Ski Hill (http://trails.mtbr.com/cat/trails-aroun … 28crx.aspx) – haven’t ridden here yet, maybe next time I travel through.
7. Collins Bay (Kingston) – if you happen to find yourself in Kingston Ontario on your way to or from Montreal.
Peter