Transporting airsoft gun in your undercarriage while crossing the Canadian/American is not an advised thing to do. Since Canadian border services restricts the importation of imitation and replica firearms they will most likely scan and notice that your luggage contains something suspicious. They will then pull the luggage and detain you to inform you that you are not allowed to bring such things into Canada, after they confiscate it they probly send you on your merry way, you may even be fined, or possibly worse.
Now that you have been informed any actions you choose do involving airsoft and crossing the border are performed solely on your own accord without support from the members and staff of this website. Please do not bring this issue up again, regardless of any "what ifs" you may have.
"Its only a little bit on fire"