Here's a couple of tips if you are crossing the US border with, and/or returning with muzzleloaders.
Make a copy of this from the CFC website
Antique Firearms Fact Sheet
If you own or wish to acquire an antique firearm, here is some information you should know about how the Firearms Act applies to firearms that meet the definition of an antique, as set out in the Criminal Code and the Criminal Code Regulations.
The Definition of an Antique
The Criminal Code defines antique firearms as:
•firearms manufactured before 1898 that were not designed or re-designed to discharge rim-fire or centre-fire ammunition, or
•firearms prescribed as antique firearms in the Criminal Code regulations. These are:
Black Powder Reproductions:
of flintlock, wheel-lock or matchlock firearms, other than handguns, manufactured after 1897; (All other reproductions must be registered and owners must have a firearm licence to possess them. For example, reproductions of percussion cap muzzle-loading firearms like American Civil War Enfield and Springfield rifles will be considered firearms and not antiques.)
http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/antique-historique-eng.htm
At the border, declare you have "muskets", ( they understand that the best)
You will in all likelyhood be asked for your "form 6"?
State polietly they are "prescribed antiques" and show copies of the following.
While they are reading this, very politely mention , that an FFL Federal firearms license) is not required to purchase any muzzleloader in the US. Again you're talking lingo they understand, very important.
Hope this helps.
Cheers nessy.