Is it possible to get a teaching job in US/Canadian universities with an NZ/Aus PhD?
Australian Ph.D. programs tend to be shorter than American Ph.D. programs because their system is similar to that of the United Kingdom; I believe that New Zealand is much the same.  This isn't "worse", just different.  This sort of difference is familiar to many scholars, and there are no special barriers to Australia/New Zealand scientists getting faculty positions in the US or Canada.  These days, of course, they will likely need to do a postdoc first, just like any other scientist.

A nice example of an Australian scientist who has done well in America is Rod Brooks, famous roboticist at MIT for many years before he headed out for greener pastures.

So why do you see so few Australians and New Zealanders in the US and Canada?  Let's start with the simple fact that there aren't all that many around, period.  Right now, there's about 24 million Australians and 4.5 million New Zealanders.  By contrast, there are about 320 million Americans and 35 million Canadians.  Thus, even if there were perfect mixing between the two countries there would be a pretty small percentage of Australians and New Zealanders in American and Canadian faculties.  And of course, it's not perfect mixing: scientists are much more mobile than many other professions, but even scientists are most likely to stay in their home country, where their professional networks are strongest and where they are likely to have good personal reasons to stay as well.  Put those together, and I would be surprised to see more than about 1% Australians in US faculties, no matter how good their education.