It's not usually "Customs duty" that one pays, when importing goods into Canada. Rather, it's sales tax. In the US sales taxes are state-controlled, so the federal govt doesn't get involved. When an item hits the Canadian border, the Canadian federal government wants their federal sales tax. As well, they have an agreement with the individual provinces to collect the provincial portion, also. Canada Post will let an item, marked as 'gift' slide, if value is less than $60CAD. Over that, gift or not, they are getting 13% for the sales taxes, plus $5 for collecting the tax. UPS typically charges $29.99 and FedEx gets, IIRC, $35. UPS/FedEx fees are on top of the 13% sales taxes that they collect and remit to the government. So, for example, a $100USD receiver, sent USPS to an AKer in Toronto is going to have the price converted to CAD, shipping charges added in, making the total, let's say, arbitrarily, $145CAD, for the receiver and shipping. The feds want 13% of the $145 or $18.85CAD. Canada Post collects that money, and adds on their own $5, for a total of $23.85CAD.
Your $100USD receiver has now cost you a total of $168.85CAD, to get it into your house. Don't like USPS/CP? Send it UPS and add another $25 or FedEx and add another $30CAD. Your $100 receiver just cost you $200CAD, by the time it gets into your house.