ONLY if you're a 'tax resident' of that country, that you have to declare your worldwide income & assets. The easily way to become a tax resident in a country (either Canada or NZ) is to simply stay for more than 6 months in a total 1 year time frame. So despite my father being a NZ citizen (as how my dad's sister's husband queried me), I explained the issue is for tax reasons for his swift departure back to NZ. (as he normally visits NZ every year but went back prior the March border lock downs of 2020).
Several years ago we had full plans for my father's return back to NZ to continue his retirement (to be closer to his family and siblings). I had an empty lot and building plans to cater for his stay. All that changed when NZ brought in FIF and more recently, the CRS, extremely inconvenient AML rules, even issues like depositing cash payment to someone's bank account at a branch is no longer allowed (have to deposit cash in your account 1st, then do your online bank transfer via direct credit). It seemed all too much of a loss in financial freedom by living in NZ.
I have a close friend that is with a Kiwi girl in Vancouver. I asked if she would ever move back to NZ and it was very clear she wouldn't. The reasons were not like how others mentioned 'for better weather' as Canada is rather extreme. The reasons were all more to do with financial matters after they consult with their accountant. Likewise with the many expat Kiwis my dad became friends with in Canada (they all moved to Canada as school teachers in the 70s). All of them have built up decent size pension portfolios and when they ask their financial advisors, they soon learn they would be taking a significant tax hit by moving to NZ. 1) deemed disposition would apply when you go non-resident in Canada. 2) though upon arrival in NZ you apply for the 4 year tax exempt status, issues like FIF kicks in. 3) not every migrant enjoys liquidating their pension funds and convert them into a NZ based pension fund.