First, I am not sure what differences there may be from the states and your province. Here in Pennsylvania, I get conflicting stories from every LEO I ask. Some claim the small cannons are classed as pistols, which I have verified is not the statute, but If you cary one concealed, you need a firearms carry permit.
As to larger ones, a few states have laws pending or passed to make anything over a certain caliber illegal. New Jersey for instance. A state police officer here told me I can own my 1.5 inch bore cannon, but can't legally fire it without first obtaining a pyrotechnics display permit. The former mayor of Lancaster PA, Charlie Smithgal owns about a dozen cannons including full size, and he fires them at civil war and other gatherings without a permit. I have checked my state laws and can't find any of the retrictions the police tell me exist. All I can say is contact your local authorities, noting the time, date, number called and the name of the person you ask, just in case they tell you worng and you are cited for something.