Your husband's family is definitely on the more extreme side in their feelings. The only people I know who feel that strongly about Americans are people on the hard-left of the political scale - usually the left-wing "activist" types that see the USA as an evil force in the world. I'll see them in the Annex neighborhood in Toronto (many U of T profs and students live there) and the like. Not surprisingly some are children of Americans who fled to Canada to avoid Vietnam so they have extra interest (and bile) towards the US.
Anyway the vast majority of Canadians are not like this. They have their own issues towards the US but as I said, it is pretty mild. I have never had an issue and if you lay low, I doubt you will too. Now if you want to walk around in your "Don't Mess with the USA" T-Shirt then maybe you'll get some stares

Otherwise they will never know. Heck, when I became a Canadian citizen and someone publicly congratulated me, I had co-workers I have known for a decade come up to me and say they never knew I was not Canadian in the first place!