Long story short, replica firearms have only been illegal by law since 1998.
It took a number of years for the government agencies responsible to execute the new law to decide whether airsoft guns were replica firearms.
It then took them a number of years more to figure out that some businesses were importing airsoft guns and selling them, when they shouldn't be. This led to a game of cat and mouse between the Canada Customs and airsoft importers that continues to this day.
No, it's not possible for you get get the appropriate authorization to import airsoft guns. They are only available for a very small list of purposes, and playing airsoft is not one of them.
"The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."