"...unless a certified gun smith does it for you..." That part is nonsense. However, I suspect the major difficulty would be finding a barrel that'd fit your Daisy.
In any case, except for toy guns that look like a real firearm(some of the Airsoft toys do and are illegal as replicas) and the muzzle velocity issue, nobody cares what you do with one. You'll likely find that a .22 cal pellet gun has less velocity than a .177. Ditto for a 6mm.
I wouldn't listen to what anybody at airsoftcanada says about the firearms laws.