Nothing.
By the law, they are Antiques there, and once chambered in a caliber not on the 'list', they are Prescribed Antiques here. Providing that they meet the age requirement as well.
From the sounds of it the RCMP are trying to push their interpretation that it is not a Prescribed Antique unless it was made in a prescribed antique caliber, but there is no law that say that, as far as I know. There is no law stating one must register it by getting an Antique Letter, either.
Cheers
Trev
