You can, you just have to know how. Possession and ownership aren't the issue, importation is. If you really want to get into the sport, or even just want "black" guns as a collector, go to: http://www.airsoftcanada.com/forums.php
Register to access the boards, then go to the FAQ section and read, read and read some more.
While you do not need a PAL/RPAL in Canada to own an airsoft gun, on ASC, you do need to be "Age Verified" (+18) to view the classified sections. The community came up with the Age Verification process as a way to help prevent minors from accessing airsoft easily and to show some measure of control to the powers that be. Keep in mind the AV process isn't required to get an airsoft gun in Canada, but it is if you want to purchase through the classifieds on ASC or from one of the retailers that sell via ASC. The AV process is very simple. Look through the FAQ for the Age Verifiers list, find one in your area, contact them, meet in person and show government issued photo ID and wait about a week or so. The age restricted areas will become available once the "switch is flicked" by one of the admins. Yeah, it's a pita and silly to have to be verified as being over 18 to buy essentially a toy, but that's what we had to do to keep the government happy, at least for now. Some guys here are pissed about the process and that they have to do it in person, but without some type of actual regulation, this is the best we could do with all volunteers. And it beats what's happened in Austrailia (no full auto airsoft guns. It was lamost banned there) or the Netherlands, where they are illegal period.
There could even be a local team with a classified section that you don't have to be verified to view or purchase from.