For gear I'd say Army Issue or One Shot Tactical. Both in Ontario.
For Airsoft parts there is Airsoft Depot, ILLusion, and Airsoft Parts Canada.
All are run by members of the site. You can communicate with them by phone or visit in person.
Lots of other spots too like Jeff just above; if someone has a particular item you want and then other big gear and accessory retail locations like Dave's Tactical or Seals Action Gear.
The real trick is to try and get your order and consolidated as possible. If you get ten things from ten places you'll be spending too much on freight.
Airsoft, where nothing is hurt but feelings.