I hate exchanging money. I never know how much to exchange. I risk not exchanging enough, more likely exchanging too much, and than having to exchange it back. And exchanging currency back and forth costs a percentage of the money.
Fortunately, many places where US tourists go will take US money. I prefer to pay with my credit card. That seems to get the best exchange rate. But some places list prices both in Canadian currency as well as US currency. For instance, at our hotel, there is a small Starbucks Coffee stand. They listed prices both in Canadian, and in US. My wife got a coffee, and I got a frapicino. We paid in US currency, but got our change in Canadian money. Not sure why as they had US money in the drawer.
This afternoon we stopped at a Dairy Queen in Niagara Falls on the Canada side. They had an ATM, but it was out of order. They didn’t take credit cards. And they didn’t "exchange" money. But they would take US money at Canadian value. So our food came up to about $18 Canadian. They would take $18 US. I did have about $6 Canadian money, so I used that, and just coughed up an additional $12 US money. I kind of felt like I was getting ripped off a little bit. I figure our food cost us an extra few bucks. I supposed we could have gone somewhere else.
But I really like to avoid using currency when possible and just use my credit card, or debit card. It just makes life easier.