
First off you would need to find a breeder willing to export. Many simply won't, but others will in certain circumstances. Usually either because they already know the person, or the person can be vouched for by someone the breeder trusts.
As reputable responsible breeders feel a lifelong commitment to their puppies and will happily take back one at any age if circumstances change they need to be even more sure with exporting, as that safety net would no longer be there in a practical sense.
So you need to get to know people in the breed who can vouch for you, get references from your vet, canine clubs, etc etc.
There are reciprocal arrangements regarding registration, so in simple terms you get a KC registered puppy, apply for an export pedigree and then can register the dog with the Canadian Kennel club.
the Canadian Kennel Club will have info on their site.
As for the practical aspects you will need to check with government agencies and airlines re age of travel, any vaccinations licences etc.
On the other hand you may simply contact/join the Canadian breed club
http://www.borderterriercanada.ca/ and source a puppy within Canada, leaving the complex issue of importing complementary breed lines to enlarge the gene pool to those who are already more deeply involved in the breeds development there.