From the CFC website:
"1. Air guns that are firearms for purposes of both the Firearms Act and the Criminal Code . Air guns that are firearms for purposes of both the Firearms Act and the Criminal Code.
These are air guns with both a high muzzle velocity (greater than 152.4 meters or 500 feet per second) and a high muzzle energy (greater than 5.7 joules or 4.2 foot-pounds). These are air guns with both a high muzzle velocity (greater than 152.4 meters or 500 feet per second) and a high muzzle energy (greater than 5.7 joules or 4.2 foot-pounds). The “muzzle velocity” is the speed of a projectile at the instant it leaves the muzzle of a gun, normally expressed in metres per second or feet per second. The "muzzle velocity" is the speed of a projectile at the instant it leaves the muzzle of a gun, normally expressed in meters per second or feet per second. The “muzzle energy” is the energy of a projectile at the instant it leaves the muzzle of a gun, expressed in joules or foot-pounds. The "muzzle energy" is the energy of a projectile at the instant it leaves the muzzle of a gun, expressed in joules or foot-pounds. Air guns need to meet both standards to be classified as firearms for purposes of the Firearms Act . Air guns need to meet both standards to be classified as firearms for purposes of the Firearms Act."
..... now in the states, they have mostly over 500 fps. Just be sure find one under. Too bad they have great deals there on 900+ fps. If life were easy, they would just allow you to show you have a PAL and cross back into Canada. But, the gov't makes things comlicated, so just be sure to be able to prove to Canada customs its not a firearm. Oh ya, and airsoft have their own rules, with serious implications (need to be clear in the center or something).