Then I will give you a primer. Handguns with a barrel length below 4 inches were prohibited in the 90s, some handgun calibers like those in .25 ACP were also banned with narrow exceptions.

For short barreled rifles and shotguns the law is different in Canada vs. The US. In the US any rifle with a barrel length below 16 inches and any shotgun with a barrel below 18 inches is regulated under the NFA. In Canada there was no such prohibition. Canadian AR-15s were routinely in the 14.5 inch range and pump action shotguns with barrels as short as 9 inches are legal.

What is very illegal, however, is hacking off the barrel. If you bought a double-barrel shotgun with 24 inch barrels but cut them down to 14 inches yourself, you committed a big crime. However if you swap them for factory made barrels that length it would be legal.

Basically you have it be any length you want as long as it is how it is made in the factory or with legally sourced factory components.