Naturalized citizens hoping to return to Canada.
Your Canadian citizenship will be valid until the day you die, unless you actively renounce it. If you were also granted US citizenship, you already have dual citizenship – you don’t need to do anything else. You have the right to enter Canada and the United States for free, forever.
No, you will not owe any back taxes upon your return to Canada. Unlike some southern countries, Canadian taxation is based on residency, not citizenship; during the 35 years of absence, you were non-residents for the CRA, with no obligation to declare.
As soon as you arrive in Canada, you can register with the appropriate provincial health system. (If it’s in British Columbia, expect a very long wait to find a primary care doctor; Alberta is in better shape.) Your contributions will be paid through provincial premiums (if applicable) and Canadian income tax.
However, you will need to carefully consider the US and Canadian tax implications of moving north. As US citizens, you will need to file US tax returns each year, in addition to Canadian returns as Canadian residents. If you’ve spent most of your working life in the United States, that’s likely where your assets and sources of income are. You could benefit from professional advice in order to reduce the total tax burden as effectively as possible and not breach cross-border reporting requirements.