I was wondering if a person living in another country who is an American citizen can open a bank account in Canada
To open a bank account in a foreign country, you usually need to be at least a resident of that country in order to qualify. It looks like this is a little different in Canada. I've found a few links that seem to suggest it is possible, although you may need to be in country to open the account.
TD Bank talks about non-Canadian (and non-US) residents opening accounts through them.
This website talks a little bit more about why you should open a Canadian account and how to do so. They do say visiting a physical location is mandatory.
This website offers some more advice but contradicts the previous link and says it is possible to open an account without being in the country, although it looks like this provides information for those who are eventually moving to Canada.
This TripAdvisor forum says that going through TD bank may in fact be your best bet for getting a bank account as a non-Canadian resident. This post specifically talks about getting an account as a tourist, and so presumably no intention to move to Canada is needed.
Hopefully through one of these links you can find what you're looking for. From reading them it appears that the easiest way to go about opening an account would be to call their customer service and inquire about opening an account. TD bank appears to show up the most, although RBC also was mentioned.
Hope this helps!