Welcome back!
Check the OFTR (Ontario Fed. of Trail Riders) site:
http://www.oftr.org/
There's a lot of links, and a forum that will likely hook-you-up with someone to ride with, or an area to check.
If you're not familiar with the Ganaraska Forest, (a bit of a hike for you), send me an e-mail.
I don't know the status of the largest area near you, Dufferin Forest. The guys in the Halton Offroad Club should have the latest info on open and closed sections.
Dave