Aturuxo: You can choose the currency you want to use with the dropdown at the bottom right of the main page (for me the option is between US dollars and Euros, I guess you'll be able to choose between US and Canadian dollars).
Paypal is probably the best method of payment here.
It is safe and most of us think GOG is a much better option (DRM-free, support, refunds...).
Unless I've missed something, Canadian dollars are not among the currency options offered here at the moment. (See the answer to question #1
here.)
carltonwalters: [...] is it safe to purchase games on gog.com is steam a better option?
As far as Steam being a better option, it really depends what your priorities are. If you want a more seasoned, stable client (assuming you want a client at all), or really like all your (recent) games to have achievements, or you must have a lot of the latest, "greatest" games the very minute they're released -- and if you're not bothered by DRM, of course -- then Steam and/or Origin would be the way(s) to go. GOG has quite a decent selection too, though it skews heavily toward older titles and indies, but the real draw is DRM free. Well, that and very good customer support
after the point of sale, not just, "Welp, you paid us, you can download your game, what more do you want from us? It doesn't work, you say? Talk to the publisher or developer -- that's their department, not ours." GOG's Support staff aren't flawless, but they do try very hard to come up with some sort of solution to any problems you might have with a game you purchased here, even if it's just, "Sorry we couldn't help you fix it. Would you like a refund?"
Going back to the "DRM-free" thing: If your internet connectivity is less than stellar, or you just don't want to
have to be online when playing your games, then GOG is probably for you. Once you've downloaded a game, you can install it and play it without ever needing to be connected to the internet (except for, y'know,
online multiplayer), plus you can just back up the installer to a disc or portable hard drive or something, and never have to download it again (unless there's a new version of the game or installer that you want to try).
Go ahead and peruse the rest of the
website FAQ, and see if any of their policies and whatnot trip your trigger.