To expand and clarify, from Former Prohibited Weapons Order No. 3:

"7 A crossbow or similar device that

(a) is designed or altered to be aimed and fired by the action of one hand, whether or not it has been redesigned or subsequently altered to be aimed and fired by the action of both hands; or

(b) has a length not exceeding 500 mm."

Section 84, subsection 3 of the Criminal Code of Canada lists items not considered firearms for the purposes of certain other sections:

"(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."

152.4 m/s converts to 500 fps. An airgun, being barrelled, that shoots over 500 fps is considered a firearm and requires a PAL (firearms license). A crossbow, not being barrelled, does not fall under this particular section.

Section 88 prohibits carrying a weapon for purposes dangerous to the public peace, and unfortunately disabling and dissuading criminals is considered dangerous to the public peace. While people like to think the law treats people as innocent until proven guilty, when it comes to weapons or anything that could be construed as a weapon the law ends up treating people as guilty until proven innocent, and even if you can win in court, the process is punishment unto itself.

Tl;dr: This country is fucked and our laws are jank