Between carrier rates, duties, taxes, and brokerage fees, a small US business might end up asking their Canadian customers to pay more to ship to Canada that the cost of the actual item. This is very frustrating because I love doing business with my fellow Canadians.
Years ago I mailed a fun little $15.00 wooden reindeer housewarming gift from Vermont to my sister in Toronto and she was slapped with an $81.00 brokerage fee! This was incredibly embarrassing and had I known this was going to happen, I would have waited and brought it with me next time I visited.
I'm always looking for good shipping alternatives to Canada and recently I found this Globe and Mail article (linked below) that gives some great options. Although this article is 10 years old now and some information is out-of-date (for example, Borderlinx is now defunct), it is still a wealth of information.
Meanwhile, I still ship to Canada but once this pandemic calms down and the US/Canada border opens again, I hope my Canadian customers will explore some of these.