That is false. Still, the USD remains the main currency for international trade and the purchase of major commodities (gold, oil, copper, steel, coffee). It is also the main reserve currency for most of the world's countries whose treasury coffers are not empty (like our). For instance, China, Japan, Russia, Hong Kong, together with several mid-east countries hold, in aggregate close $3T (3,000,000,000,000) in US dollars.
Now it would be very odd for the issuer of the currency to switch to Canadian dollars. If we abandon our own currency, that would be a serious blow to our national confidence, triggering systemic crises around the world.
That the Canadian dollar has become so strong (initially a source of pride for Canadians), has now translated into trouble as many Canadian companies are seeing their export market evaporate. Canadian goods have become too expensive.
As for a day when the USD will not be the reserve currency of the world....well, some are forecasting that if we continue to spend money we borrow from foreign investors as we do (believe it or not a great deal of US mortgages, credit cards, and student loans are funded by international investors), the day when the Euro and a basket of other currencies push out the dollar as the main reserve currency of much of the world, is a lot sooner than many realize.