When I travel to a foreign country I take the coin of the realm to use. Canadian money in Canada and US currency in the US.
Taking US money in Canada is done so as a courtesy. For a retailer, a form of business I was in for 40 years, exchanging foreign currency can be costly unfortunately, making for some not so amicable verbal exchanges at times.
On both sides of the border we start off with a few dollars, generally left over from a previous trip. Then on our first shopping trip we will get cash back. This avoids service fees at the ATM and use a debit or cash card that gives you the best rate of exchange.
That seems to work the best for us and I have heard of lots of folks doing on both sides.