Check out the "ontario" subforum under "Events".
When a game is organized, often people will make a post there, and you can "sign up" to attend.
If you just want to try out your guns, in a walk-on game, check out Ultimate Airsoft (www.ultimateairsoft.ca
), near Downsview Park.
Some Friday nights, TTAC3 has a game, in a building space located at Ossington and Dupont - keep an eye in the Ontario events section, as a post announcing if there will actually be a game on Friday, will be posted there.
Other than UA and TTAC3, most games are organized at outdoor locations.
Edit: ninja'd by ShelledPants