GHK products are by far the best GBB IMO.
MilSig has a horrible reputation because they over-charge by 30-50%, and offer 30% off when they do "specials." - SOMETIMES they have OK pricing.
Toronto Airsoft is two fold, most people tend to not order from them, but they have a lot of walk in customers.
There's a bunch all over, you'll need to do your homework about retailers in Canada, and international.
Getting AV'ED is a good idea, but the wait time is 30-60 days AFTER you meet with a rep, since it's a volunteer basis. If you're looking for used, you can check out the cancerous group on facebook. https://www.facebook.com/groups/realairsoftcanada/
Careful buying used on there though.