If you are taking back anything major that you bought there, you are supposed to declare it.
E.g., I bought a kayak in Canada. When I took it back, I declared it. There was a benefit: sales taxes in Canada are much higher than the U.S., but I was able to get them back by going to the Canada-side office.
BTW, though this is years ago, the U.S. side searched the kayak, which meant I had to go a location they set aside for doing this, take the boat off the roof racks, let them look inside, and put it back. In general, they may do searches, and you should allow time for that. In fact, there may be a long slow line at the border.
Some U.S. auto insurance companies may not cover driving in Canada, and vice versa.
Figure out before you go a table of speed conversions, so you don’t accidentally go over the speed limit. It’s probably a bad idea to get a speeding ticket in another country, because there is a risk they might make you stay for paperwork. (I don’t know this for sure - I made a point of staying within the speed limit so I wouldn’t find out.) If this hasn’t changed, Canada has some really good extremely long highways along the U.S. border which have relatively low speed limits. To some extent Canadians ignore them, but as a foreign visitor, I guess you shouldn’t.
Canada is a very beautiful country, with a lot of open wilderness. But if you go into Quebec, it may be helpful to speak French - I don’t know, haven’t been there since a child.
Don’t use the term “America” or “American” to refer to the U.S. - they are Americans too, and a few find that insulting.
Also, check paperwork, recent requirements for going AND coming back - they might possibly include birth certificate, passport, driver’s license, proof of applicable vehicle insurance, Covid vaccination requirements entering the U.S. (??) - look it up.
Maybe check
https://travel.state.gov/content/travel/en/traveladvisories/traveladvisories/canada-travel-advisory.html
before you go.
But my info is out of date.