In the thread 'A Big Ol' Airsoft Q&A' by HonestJohn written in 2008, http://www.airsoftcanada.com/showthread.php?t=51609
, pretty much makes it clear that airsoft is illegal but is an unenforced law.
However In the thread 'Airsoft and Canadian Law - Important Readme for New Folks' has a reply written by RecceGod in 2006 , http://www.airsoftcanada.com/showthread.php?t=23034
, RecceGod shows a part of the Criminal Code and Weapons Act which states that certain weapons deemed not to be firearms include
(d) any other barrelled weapon, where it is proved that the weapon is not designed or adapted to discharge(i) a shot, bullet or other projectile at a muzzle velocity exceeding 152.4 m per second or at a muzzle energy exceeding 5.7 Joules, or(ii) a shot, bullet or other projectile that is designed or adapted to attain a velocity exceeding 152.4 m per second or an energy exceeding 5.7 Joules.
So if an airsoft firearm fits within these requirements then it it isn't a firearm and therefore cannot be called a replica firearm
The legalities of airsoft seem to be stuck in some sort of pardoxial grey area.