It rather depends on where and when in Canada.

In Québec once you're identified as an American rather than an Anglophone Canadian, folks are friendly, especially if you can also speak some French.

In British Columbia, Alberta, Saskatchewan, and Manitoba, generally no problems.

Ontario .... well, during the Vietnam War it could get rather touchy.

If Americans had heard or read of Justin Trudeau's "Those qualities are what make us the first postnational state", the sympathy would be going in the other direction.

Unfortunately most Americans are profoundly ignorant about Canada, whose national capitol varies from Toronto to Montréal; please accept an apology.