Whoa, the greenback may be a world currency in the US but its acceptance in Canada had been due to the fact that it was worth relatively more at one time so folks could make a profit. Try to pay with Euros in NY, even though they are worth more. They are regarded as another unacceptable currency because they aren't green. If God meant currency to be colors other than green, she would have made real money in those colors.
In general, I haven't witnessed most countries being all that accommodating toward people paying in foreign currencies. To give one example, when I was last there, there were a few shops in London where you could spend Euros at rip-off exchange rates but you need to have GBP in most places. It's extra work to train cashiers to recognize counterfeits and for the cashiers and bookkeepers to keep track of foreign currency transactions, separate the foreign notes and coins and arrange cash transfers to the bank.
Canada has traditionally been cheap for Americans so there are a lot of Americans who cross the border on short visits and want to spend their USD and businesses find it profitable to accommodate them. New York gets tourists not just from the Eurozone but also Canada, Latin America, the UK, Japan, Russia, the Middle East, etc. No way can anyone keep track of such diverse currencies and plus buying rates of foreign currencies in the U.S. tend to be poor for some reason.