Unless there is a specific clause in NAFTA, there are no duties on products *made in* the US or Mexico. Products made elsewhere but sold by a US business may invoke a duty, as it's the country of origin (COA) that matters, not who sold it.
NAFTA is 2000 pages long. But as far as Canada goes, there is the limit on dairy, and there is some protection of cultural items. For example an import CD versus one manufactured in Canada, or the requirement that subtitles in French be done in Quebec or face a duty (mostly affects imports from France). No agricultural limits, no lumber limits, no sugar limits (to mention areas where the US imposes duties or tariffs from Canada).