I find that in cities near the border, Canadian and US coins are interchangeable and usually accepted at par. In Toronto there are a fair amount of US coins in circulation, and I've never had an issue using them here.

Helps that each of our coins are almost exactly the same size and weight for all common denominations.

I just got back from Whistler BC. Because Vancouver tends to take USD, and Whistler is not far (and is even more heavily touristed by % than Vancouver, I'm sure), I figured we'd have no problems with USD.

Mostly we paid with cards, but my wife brought a few US$100 bills. It was silly to try to spend them for small purchases, but one night we had a CAD$60 dinner and we asked if we could use USD (hadn't been a problem anywhere else). They said yes, BUT they'd only accept it at 1:1. Obviously that's their prerogative, but it seemed silly to expect us to eat $18 or thereabouts, so instead they ate the credit card transaction fees. shrug

Granted, this is probably not bad policy in general because they're going to be even less expert at spotting fake US currency than US-based merchants are.

The toll both machines don't accept them even though the coins are superficially quite similar.

Where I grew up, in MA, canadian coins were accepted, generally.

I'm in a city now and I've had people refuse to accept 2 dollar bills (which are rare, though absolutely legal tender).

Steve Wozniak's hilarious book of perforated $2 bills: https://www.youtube.com/watch?v=LJ1TIYxm1vM

You can buy it here: http://www.moneypads.com/products.html

I've done it both ways with Korean and Japanese coins because they look nearly identical, I assume due to the colonial past. The values differ by 10x.