They are the only G7 nation (and I use that word cautiously) to have done this.

They rely exclusively on the United States for a crisis, making no pretense to being able to stand alone. 71% of their sovereign financial reserves are held in US Dollars.

(Side note: Militarily, their army is the equivalent of the New York City police in terms of manpower. We fly them when they want to go somewhere. They do have some decent air power that they buy from us, which is great, but hopefully they are not buying on credit.)

I found it amusing in the movie Civil War, when the gas station accepted Canadian dollars rather than US dollars. If the events in that movie were coming to pass, the Canadian economy would be trashed, and the Mexican Peso would be stronger than the Canadian dollar. I recall something ridiculous, like for every dollar in foreign reserve currency Canada holds, Mexico holds a ton of gold.