It is always helpful if you state facts, when raising such questions, whether you are a visible minority or not.  First of all, a Canadian citizen's child,  born outside of Canada, is not a Canadian Citizen unless their parents were themselves born in Canada or who were first immigrants. So they can't just move back. I was born in Canada.  If I have a child born outside of Canada, their children (my grandchildren!)  born outside of Canada are not citizens.
Second, after immigration to Canada, a person must stay in Canada for two years out of five, or they lose status.  To get citizenship, you now need to be in Canada for three years out of five.  There is no escaping the rules anymore, now that the eTA system is in place.  
Finally, there is no evidence existing anywhere that the 3.0 million Canadians living outside of Canada are coming back - in fact, the numbers keep growing. There are a lot of facts that explain why - you should check them out before assuming the worst.