Ok, time to weigh in here.
I used to own an importation/wholesale airsoft company, and here's what I was told, and how I legally brought in launchers:
First, does it 'resemble with near precision and actual firearm (launcher)? If yes, then continue, if not, it could make it in with no issue. If it looks like an existing launcher, then it will be scrutinized. This is where it gets a tad tricky and possibly even silly. If there is no shell shipped with the launcher, then it cannot be tested, therefore (according to the CBSA) it's a 'replica', which is prohibited and in need of specific licensing. If it is shipped with an airsoft shell, all normal airsoft import rules apply; must fire at least 366fps with a .20g bb.
So how did I legally import them, back when the velocity for airsoft was up at 407fps? Here's the silly part; when shipped with a paintball shell, it was considered a paintball launcher, and not subject to the same scrutiny as airsoft launchers. Exact same launcher, different shell, but the combination allowed for legal importation with no hassle.
To sum up: launcher alone = prohibited, launcher + airsoft shell = must shoot min. 366fps with .20g bb, launcher + paintball shell + shipped as 'paintball launcher' = imported successfully and legally every time.
Now, I no longer own the company, and have not personally imported a launcher since early 2013, but the above was valid at the time.
The Tier One Tactical Operator
Tippmann Arms M4A1
KWA USP .45, KJW P226, KJW hi-cappa