So in Canada, muzzle loaders fall into three categories - all other firearms fall into one of four categories.
Antique firearms require no licence.
Non-Restricted firearms require a PAL (possession and acquisition licence).
Restricted firearms require an RPAL (restricted possession and acquisition licence) and,
Prohibited firearms require a "grandfathered" rider to an RPAL. (allows people who owned something that "went prohibited" to continue to own it and others in the same class/style)
In Canada a ML pistol is a "restricted" weapon. Doesn't matter if it's flintlock, caplock, wheel lock etc, it's treated exactly the same as a brand new Glock off the shelf. So even a pistol "kit" would be considered restricted (as are some components of modern firearms even if not complete - some "lower receivers" are restricted and others are prohibited, all by themselves)
Without going into the ton's of red tape and regulation, essentially a ML pistol, or enough components to constitute a pistol is generally a "no-go" for an individual (would have to use a licensed importer along the lines of your FFL dealers).
A barrel shorter than 14" would always be considered a pistol barrel by our customs and firearms center regardless if it was for a modern or antique arm, thus a "restricted" barrel - and it doesn't matter that it's simply a "tube with a hole in it".
One could try importing an 8" piece of 12L14 "tube" but if customs discovered it was actually a pistol barrel "life would not be good" for the importer.
So basically then we are dealing with either flintlock (or earlier ignition systems) and caplocks in the form of long guns, plus their components.
In finished form (or "functioning" form) a flintlock or earlier ignition is considered an Antique firearm even if was built yesterday so it is NOT a firearm under our firearm regulations - so no restrictions at all - just like importing a box of pencils.
Components to build a flintlock from the barrel, lock and onward, are simply treated as "stuff" - again, could be a box of pencils.
A functioning caplock is considered a "non-restricted" firearm. To import that it would/could be held at customs until proof of a firearms licence is produced.
But, we can import all the components to build that "long barreled" caplock totally unrestricted, again as easy as a box of pencils.
Once it's all "assembled" the flintlock is still not a firearm (under the firearm regs) and the caplock is non-restricted, requiring a licence to own.
Since I personally only hold a non-restricted firearms licence, if I chose to say lop off 8 inches of barrel from a long gun and make a pistol with it, I would then be in possession of an "illegal" restricted firearm.
Up here if you want "any pistol" it is possible to own them. But complying with all the requirements is very onerous. And they can only be discharged on a government approved range requiring a permit to move it from your house to the range etc etc etc.