There are no New Zealand seats, all are imported. New Zealand does accept other countries' certifications. This site has info:http://www.childrestraints.co.nz/standards.php
European and Australian seats seem to be automatically certified, or can be used without certification, the American need NZ certification. But I would actually be surpeised if anybody except LTSA knew this, including the police. I'm quite certain "Illegally imported carseats" really isn't anything the New Zealand Police has any interest in.
Not to say you should do anything illegal, at all!
We have a European-certified (Scandinavian) seat, bought here in NZ, but only certified in Europe. For any questions, please contact Land Transport Safety Authority (LTSA), they should be able to answer any questions. If the Canadian seats aren't ok (would surprise me, but hey, what do you know?), I'd get a good Scandinavian seat.
If you can't find an answer, pm me, and I'll find out.
LATCH is probably not common here, most cars sold in NZ are second hand cars imported from Japan (this is where Japan sends there used cars). Almost all cars need the seats to be installed with belts (and whatever the seat comes with, our car seat latches on around the seat in front to sit sturdy, which works on all cars), and most can have the tether straps that go over the child and seat when rear-facing.
The law says: Children under 5 years old
* Must be properly restrained by an approved child restraint.
* They must not travel in the car if you can't put them in an approved child restraint.
* Must be properly restrained in an approved child restraint.
Plunket (the organisation that does the Well Baby visits, check ups etc, mighty important here!) recommends rear facing to age 1 and 20 pounds ( think - we don't do pounds here). And a baby capsule has to be rear-facing, of course. Otherwise, you are free to put your 9 month old in a back-less booster, provided his weight is high enough for it.