I mean, the dude you replied to is pretty much correct, not to be a debbie downer.
In theory, any gun advertised as shooting 366FPS or higher with a .20g BB should make it across the border. A lot of the times, this doesn't matter. The CBSA could just decide to not allow an airsoft gun because they don't feel like it that day. Unless you want to spend a lot of money on a shipping broker/lawyer, you're essentially SOL.
As someone who works for a retailer, we have had experience from bringing guns in from the states from distributors, and unfortunately there's been a load of "cease and desist" orders from the CBSA to specific american retailers and wholesalers. This is why Evike no longer offers the "Canadian border approval package", and why we can't get airsoft guns from Jag Precision. They both fell victim to this.
Also, from my experience, CBSA don't chrono guns themselves. More often than not, they google the gun from the manufactures website (if they even have one), read the velocity on the website, and deny or approve based on that alone.
I've only had experience ordering rifles from outside of Canada (and only Hong Kong, for that matter), and I haven't personally had issues. I have on the other hand, heard only horror stories from people who attempt to order KWA handguns, Tokyo Marui rifles, and the like.
Now do you know what gasses they use or no?
The reason why he didn't tell you what type of gas they use, is because they don't use any at all.