Everybody coming into Canada, especially those who are a permanent resident or who holds citizenship (and I think Student/Work Visas, correct me here) are required by law to declare anything they are bringing in that they have purchased outside of Canada-this is for duty/tax reasons.
Since you are studying here, I'm assuming you fall into the category of Student Visa, which is covered by the following:
When arriving in Canada for the first time, you can temporarily import your personal and household effects free of duty and taxes. These items include furniture, tableware, silverware, appliances and motor vehicles. Though these goods are not normally subject to duty and taxes at the time of importation, the CBSA may require that you post a refundable security deposit. The following conditions apply:
* The goods cannot be used by a resident of Canada;
* You are not permitted to sell or otherwise dispose of the goods in Canada; and
* You must take all non-consumable items with you when you leave the country at the end of your temporary residence.
That is directly quoted from here: http://www.cbsa-asfc.gc.ca/publicati...f5068-eng.html
The article above also state procedures to temporarily import your stuff, which is important. At the least you should take the time to compile the list as it says. Do read it!
Regarding airsoft specific items, they are personal effects, and as long as no full black/full steel receiver containing the serial number of the rifle/gun is imported, you should be fine. The magazines and stuff that might be misconstrued as ammunition you might have to make clear so as to not confuse them. Everything else is fine. The most important thing about airsoft in Canada is that you CANNOT ship IN the part which the government defines as the rifle, which is the part with the serial number. In most Armalites, that's the lower receiver, but on such guns as the MP5, the upper is the restricted part.
On leaving, there won't be a problem.
Enjoy your studies here!