Please read my questions again.
If someone buys cryptocurrency/ owns cryptocurrency before moving to canada then that means it is his capital before he become resident of canada so he should not be liable to pay tax on it in canada as this is the income from another country. no?
If you are a resident of a country at the time of selling your asset in their country then you are liable to pay taxes which can be whatever the rate the government proposed. But there are some countries with no tax policy which can be helpful for you in that case or else doing the trade-off the radar like via physical cash and nothing with bank account then you can avoid it too (illegally).