The United States imposes tariffs (customs duties) on imports of goods. The duty is levied at the time of import and is paid by the importer of record. Customs duties vary by country of origin and product. Goods from many countries are exempt from duty under various trade agreements.
You’ll need to pay customs duty (or import tax) on any goods you move across the US border from other countries, THOUGH goods from some countries are exempt due to different international trade agreements.
The United States Customs and Border Protection (CBP) enforces customs rules.
NAFTA is dead … we have a new United States–Mexico–Canada Agreement “USMCA”. I have not had the opportunity to research nor confirm if anything has changed from NAFTA w,r,t. audio equipment in general, or issues (if any ) from origination in other countries outside of NA,
And that is without prejudice to any favourable or lucky experiences others may have enjoyed under them”old rules” because of administrative and favourable laxity of rules applied by Customs for shipments using CANPOST to USPOST instead of large private carriers ( eg FEDEX) who have their own customs clearing houses and generally “go by the book” in detail.