At least in the US we are taxed globally but you deduct any taxes paid to foreign governments from US taxes. So if I owe the US $10 and pay Portugal $8 in taxes, I pay the US $2. My total tax burden is the same.
Canada and NS may be different of course, this is just as an example of how expat taxes can work. I highly encourage you to get advice from a tax professional and a lawyer who specializes in international tax arrangements.
Also almost everywhere I have ever lived has taxed people when they move based on their intent. I know for Portugal at least that we owe taxes when we arrive if we intend to stay for more than 60 days. We owe those taxes immediately, not after a period of time. I imagine you will pay a full year of tax in each of those countries, not only after 180 days.