Ok, This is what I have found: (I'll try not to make this too long)
A homemade cannon falls under the definition of a Firearm under sec 2 of the Criminal Code of Canada ("a barrelled weapon from which any shot, bullet or other projectile can be discharged and that is capable of causing serious bodily injury or death to a person, and includes any frame or receiver of such a barrelled weapon and anything that can be adapted for use as a firearm")
now, under the FIREARMS REFERENCE TABLES, a homemade cannon described as a single shot having 2212mm barrel 2 1/2" percussion calibre, fired from a 209 percussion cap ignition system, features may include a bronze or steel barrel, two wheel carriage, system of elevation, breech plug, has an FRT# 126426-1 and is NON-restricted.....so falls under the same regs as all other non-restricted firearms, just keep the barrel length as a non restricted, non explosive/incindiary ammo, etc. Now classifying as an antique due to ignition systems may be different and nothing is mentioned in my literature and that call would be up to the Chief Firearms Officer through the CFC for your area, but like I say why not call it unreg and get the reg cert and then you'll have all the proper paper you need....just in case.
Oddly enough when digging in the frt's I found that an RPG-7 IS NON-RESTRICTED.....the explosive ammo is just prohib under many different laws, but a training round on the other hand is not explosive, so no problem.....u just cant carry it into a bank or the supermarket or somethin thats all....found that interesting
hope this helps, amy more qustions just ask, I'll do my best....