Right, let's clear up some misconceptions and questions about the UPS brokerage fees. Bear in mind that this is from a purely Canadian point of view.
1) It is NOT import duty or tax. It is NOT levied by the government. It is a fee that UPS charges.
2) The reason they charge this fee is: paperwork. When a parcel's total value is over $20, it is subject to import taxes. In the case that your package incurs import taxes, UPS acts on your behalf - as a 'broker' - signing the papers and paying the taxes. For this 'service', they charge you not only the taxes they paid, but a brokerage fee on top of it.
3) For shipments by air, the brokerage fee is always $10.
4) For shipments by ground, the brokerage appears to always be $6 - however, there is also a $7 'entry prep fee' that is applied to ground that is not applied to air.
5) GST is also applied to the brokerage fee.
6) UPS will ALWAYS CHARGE brokerage if your package is over $20. Always.
I've attached two typical brokerage invoices from my brokerage account with UPS - one air, one ground.
So, how does that differ with USPS? Firstly, there is no brokerage fee. You pay any applicable taxes or duties upon receipt of the package, plus a small handling fee that varies with the size and weight. This happens occasionally. Canada Post will not ALWAYS charge import taxes - they do so randomly.