I was never called a Canuck myself, but definitely a "Newfie" which some Newfoundlanders may see as a insult, depends on how it is said. (very rare someone takes offense)
I heard of the term "Kiwis" before, but never "EnZedders", as far as I know a Kiwi is a symbol for NZ, so I doubt that is seen as a insult.
That would be a interesting discussion, I know a lot of Americans pronounce Newfoundland wrong, wonder how people from England would pronounce it!