Usually they're paintball venues which airsofters get second dibs on since the paintballers are "what brings in the money" for the field owners (I understand completely, they still need to run a business you know).
However there are a few dedicated fields, TTAC for one which does indoor CQB games. Other than that sometimes someone with contacts can organize games at abandoned hospitals, factories, and such ("Border Wars", "Claybank", and "Cold Front/Keystone" for example). However it's not advised you go to any abandoned buildings with a few friends and start shooting at each other since a lot of planning and such must go into these games before you can even think about stepping foot there.
Basically this forum is a "meeting place" for airsofters around Canada, there are local club forums such as Op-For, BCAC, JOC etc. However as a national forum this kind of represents airsofters in Canada (not to mention some US and European players).
So when you go to get AV'ed you'll show the AV rep your DL, Passport, whatever and they'll make sure who you say you are and that you're really 18+. Once thats done they'll record basic details, basically your name and input it into the "system" on the forums. Once thats done a site Admin will add your name into the database and you'll get your cool tag. This process can take upwards of 2 weeks, since the Admins usually add your name into the database in batches. That's basically the process that I understand it as there may be a few more things that happen but thats essentially what it comes down to.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE