[FirestormX]

In terms of pistols, they're actually pretty simple, for the common pistol models:
Buy Tokyo Marui (plastic) or KWA (metal).
If you don't have the money for it, buy KJW.
If you can't find a KJW, buy a WE.
If your WE doesn't shit out on you in the first few games, buy a lottery ticket.
Avoid absolutely everything else.

I should mention that KWA and KSC are usually the same product. KSC is primarily sold in Japan, while KWA is aimed for markets outside of Japan. There's all sorts of other threads on the internet, full of a bit of fact and lots of speculation. But for the most part, a KSC and a KWA are on par with each other, and you can google the specific pistol model that you want to buy in order to find out if there's any differences.

For gases:
If you're playing indoors, and it's going to be warm, run green gas (propane). It's cheaper and easier. Most people will run green gas outdoors too, weather permitting.
If you're playing outdoors in the cold, or want some extra FPS without modifying the gun, go with CO2. Make sure your gun can handle CO2, of course. Don't go putting a CO2 mag in a TM.

Some people also like CO2 because they don't have to refill their mags with gas after emptying it each time, and because they can load up a shotgun card with CO2 canisters for refilling on the field. But you can just take along an AI gas can for that.

In terms of the what common pistol models are available in Canada, you have the following platforms (and their variants - there can be a lot of variants):
M9s
1911s
Hicappas
P226s/P229s
USPs
Full sized Glocks
Compact Glocks
Subcompact Glocks
XDMs