Technically the guns are legal for import as an unregulated firearm, due to their FPSes. But of course, but it's up to the CBSA agent to decide whether to seize it. Their primary method of determining if it should be seized as an imitation firearm is to check the manufacturer's specs (usually online, or in documentation). They generally disregard any note that the retailer attaches with the product that says "this has been upgraded to shoot within the legal limit of an unregulated firearm", for obvious reasons.
So it is perfectly legal to import these guns, but usually isn't worth the headache of the seizure.