As an individual, credit could only be obtained from a UK address, so then they can and do serve to last known UK address.
However, if you were a business, then different rules apply, as it is possible to obtain UK credit without a UK address, but as that would be a business matter then CPR 6B would apply, even if not in the EEA
As for enforcement CCJ are sold abroad, and there have been many cases where they have been sold into the USA, chased in the USA, and the debtor sued in the courts with them.
As Canada and Australia are both commonwealth countries, it is my understanding that reciprocal laws are in place for the pursing of UK based CCJs
It will come down to what reciprocal laws are in place and that is definitely well beyond the remit of this forum.
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My advice is guidance only, if you want the law then consult a lawyer!
(c) All Spelling mistakes are my own design, infringement of them may result me sulking!