Up to this point, Cdn citizens crossing the US land border from Canada, say to catch a cheaper flight out of a US airport, just vanished off the govt's radar. That's what's coming to an end. Anyone catching an international flight from a Canadian airport was already flagged as having left the country.
As for Healthcare, Canadians have for as long as I know faced exclusion limits put in place by their home provinces if absent from the province/country for more than a set period of time. However, this is Canada. I cannot see the healthcare system denying a Canadian citizen urgent/required medical treatment if they present themselves at a Canadian Hospital regardless of how long they have been out of the country. Asking the govt to pay for treatment accessed outside of Canada is a different matter.
Access to Healthcare is not a right but is enshrined in our culture and legislation. Any Canadian automatically qualifies for healthcare upon returning to Canada and the expiration of a waiting period that is no longer than 90 days. With this certainty of payment by the system, there is no point for the hospitals to jumping up and down.
Those living outside Canada have a choice. They can declare themselves non-residents of Canada for tax purposes and enjoy a lower income tax rate. You can also declare yourself a resident for the purposes of taxes, if you still maintain significant ties to the country (bank accounts, own real estate etc). You are assessed for taxes at the full rate and may derive some preferential consideration based on that status if you suddenly find yourself back home.