Crossing the border into Canada isn't like it used to be.
Here's some info from AAA. In addition, I'd recommend talking to your bank to see if you can get some Canadian currency before you leave the US. If not, your local American Express office can convert some for you. The smallest denomination for paper money is 5$ CN, but they use $1 and $2 coins. (Loonies and Toonies). Once you leave the border area, restaurants, grocery stores, etc. in small towns won't know current exchange rates, and may not even accept US dollars. Happened to me. Gas stations accept credit cards, but when I went through, you couldn't pump your own gas. Attendant required. Tim Horton's is the place for coffee and they're everywhere, like Starbucks here.
Also, if you're a smoker, hide some US cigs in your rig from customs. They're very expensive in Canada. (And I didn't tell you that).
Canada uses the metric system.
Here's a link to conversion tables. That got me once in a deli. They were selling lunchmeat by the gram. So I just ordered 8 slices. Mile markers are Kilometer markers north of the border, those are on the speedometer on most US cars, but if you're approaching an underpass, you need to be able to convert meters to feet quickly. I just put a sticky note on the dash with the height of my rig in meters.
Now that I've convinced you to stay south of the border - don't. Its a beautiful country and an adventure.
Retired and visiting as much of this beautiful country as I can.