In my experience, most Canadian businesses in major population centers, especially tourist areas near the border, are happy to accept US currency. Though they probably stiff you on the exchange rate.
That’s been my experience, and it’s not even an extortionate exchange rate, it’s just a not-very-good exchange rate. Now… trying to change dollars to euros at the airport (in the US or in Germany, the two places I’ve priced it recently) is truly extortionate.
The proprietor did not seem to speak much English, it took quite a bit of pantomime to convey that the reader wasn’t working. I showed him my American cash, and he shook his head, “no.” So I said, “ATM?” He nodded and pointed across the street. And that’s how the tiger got its stripes I paid for dinner.
A couple of years back, I spent a couple of weeks in the town of Leticia in Colombia. It’s on the shores of the Amazon river, not connected to anywhere else by road, and is placed right at the tri-point between Colombia, Brazil and Peru, which has no border checks between the countries if you stay in the tri-point area. There’s also a town on the Brazil side, you could walk down a street to Brazil (in a different time zone, as it happens) with not even a sign to indicate that you were now in another country. The Peru border is mid-river, with a smaller town on an island, so you couldn’t do that accidentally, but again, no checks. The only immigration checks happen if you leave the area by river or by air- you can travel freely across the river and to nearby ports.
Anyway, all three currencies were freely used within the area and accepted by everyone, despite being of completely different values (didn’t see so many Peruvian sol, but their town was the smallest with no airport). At one point I got a little river boat back from the Peru side to Colombia, paid in Colombian pesos and got my change in Brazilian reals. Currently, the exchange rate is roughly 1 Sol = 1.5 Reals = 1090 Pesos.
I’m sure I got short-changed constantly. The kids there must grow up great at mental arithmetic.
I went on a school trip to Europe about forty years ago. Our last night, before flying out of Frankfurt, the guys had a big poker game, using all our leftover Pounds, French Francs, Swiss Francs, Lira, and Deuchemarks.
I remember when it was an at least semi-regular thing for the stewardesses on airplanes coming back from Europe to go down the aisles with a marked envelope and collect stray coins/bills from whatever countries as donations to Unicef.
I have seen collection boxes like that at airport terminals.
Years ago, our family was visiting London years when we found ourselves with a few extra days. One day we went to the city of York on a high-speed train (Eurostar?) We returned that evening so I went to the lounge car for a beer (it was getting to be a long day visiting the sights). The sign said it would be something like 5 Euros, 5 pounds, or 5 US dollars. Wow, I didn’t expect that! I had a five dollar note with Lincoln’s portrait on it, which they gladly accepted. A Belgian beer on a British train, paid with American money.
This was a while ago, and I wonder if they still do that.
Very common here in Michigan to see Canadian coins given as change. Everyone treats them as interchangeable with US coins here. I say everyone, but one time back in the 1980s I was working at an ice cream store and was making change for a customer who was apparently from Texas. I handed him 22 cents change, which included a Canadian dime and penny. The guy held the coins in the palm of his hand, then held them up and stared at them in a sort of contemptuous wonder, like I’d just tried to pass off coins he could never use as currency, like Madagascar francs or Syrian piastres on him. He then angrily and loudly demanded “can I get that in AMERICAN MONEY”? Everyone in the store turned around from their desserts and shot him a wtf look.
I remember once receiving a Brazilian real in my change in lieu of a (Canadian) quarter. I insisted on receiving a real quarter instead. Later I looked up the value of the BRL and it was actually worth more than a quarter so I short-changed myself.