from Canada, its all about the lifestyle and the weather. These are inter-related. In Canada there is a very small window of time each year to actually be physically comfortable outdoors. Bad outdoor weather has an effect on your mood. Canadians spend the vast majority of their lives indoors. There is a lot of weather related depression in canada, diagnosed, undiagnosed, and unrealized.
NZ is much more laid back work wise as well. far less of a rat race in NZ.
Also, depending on your industry, you may or may not have much better work opportunities in NZ (applies to me in a big way, for this moment in time anyway)