I'm not sure we're going to be helpful in regards to what you can get for your store, most of us want the stuff that is really hard to find (things that are still legally grey) like full metal AEG's and GBB's.
But if I were you, I'd be contacting airsoft distributors. See what is available to you as a canadain retailer, you'd be suprised how many there are. As for what we're looking for? Full metal!! good quality, mostly mid to high end with some low end beginners stuff. Preferably full trademarks but that you can't help. A plethora of accessories (mags of all types and sizes mid caps espacially). AK's M4's MP5's ect. the most popular types and make sure the parts you sell match the guns you've got. Example: Don't get a bunch of clearsoft M4's and then sell only MP5 accessories from TM or something dumb like that. (believe it or not I found a site like this) Get a wide selection aswell people like having a choise. As for brands G&G are decent mid-quality some say upto high end) I know real sword is good. there is actually an article on this here at ASC I'll link it if I find it again.
Also bring back the AEP to Canada I miss those things. only clearsoft AEP's around now and that blows goats,