There is no Canadian duty on U.S.-made audio gear. NAFTA assures that. However within Canada there are federal and provincial sales taxes imposed on every purchase except some held to be basic necessities. Audio gear is not held to be a basic necessity, so taxes have to be paid when you buy it, no matter whether you buy it in the States or in Canada.
That means that when any audio gear crosses the border from the U.S. to Canada it will come with a tax bill based on its declared value.
There may be other fees also. If the gear wasn't made in a NAFTA country it may have another 6% duty imposed. In addition there may be brokerage fees, depending on the carrier's policies and rates.