If you try to import one, the information that the CBSA will go by first and foremost is the information printed on the box or in the owner's manual that comes with the gun stating it's velocity. If the box has anything other than 407-499 fps, it will be seized, end of story. If it gives an energy rating as well (rare) that states anything like "1J" (as is required in Japan and many other countries) it will be seized, end of story.
If the gun does not have the 407-499 fps on the box or in the owner's manual, and does not show any velocity at all for example, it will be seized. You can not convince the CBSA of what it shoots, they will not listen to you, nor to airsoft reviews, nor to Redwolf ads for the gun.
I can tell you now that I have not seen 1 gun that has the required info printed on the box or in the owner's manual, not 1 out of hundreds.
Now, you can get cheeky and let the gun get seized, and then hope to fight it on appeal knowing that you'll win because of the actual performance of the gun. But the CBSA will send it to the RCMP Firearms Forensics Lab in Regina for testing. You have no control over the test procedures, nor to you have any way to know the actual performance of the gun. You can expect the whole process of seizure to final CITT appeal to take up to 5 years. In the end, they may miraculously find that it shoots 406 fps, oopps!! Too bad. Appeal denied. Did I forget to mention the costs involved for a $450 U.S. gun to be heard through years of appeal? Contrary to stated CBSA policy, the appeals are not entirely "free of charge". If you want to have counsel present during the CITT portion to present evidence, that costs $$$.
This is why your idea has not historically worked, why Peter Kang allowed 2 guns top be seized intentionally so that he could fight them on it, but still lost anyways. This is why, although the 407 fps threshold has and still exists for airguns, you will not have a very easy or successful time using it for airsoft.
The 407 fps thing is not law at all, rather CBSA and RCMP policy that is not open to change, unless you get Parliament to institute change. This will not come from 1 measly CITT case, or even a court case for that matter.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.