i am a senior manager in the industry, so here is my take and some clarifications
1) USPS/Canada Post is clearly the cheapest way, if you have the time. The brokerage fee is subsidized by your taxes so its cheaper than the commerically operated carriers.
2) Anything over $20.00 requires reporting to Canada Customs. UPS does this on your behalf and since they are providing a service to you at an expense to them, they are entitled to charge you for it. If you want to argue about how much of a cost it is, we could be here all day. They have invested in people on staff and technology infrastructure to provide the clearance and automate the reporting.
3) It is illegal for commercial carriers to charge the same price as the Post Office. As in point 1, the Post Office is subsidized by the taxpayers, nothing wrong with using them since you are already paying for it.
4) Purolator mostly uses DHL for their International shipments. DHL has a great network but lousy customer service which means if your parcel is lost, dont hold your breath.
5) While you arent obligated to use their clearance service, some companies will charge you to transfer the paperwork to another commercial broker. Not sure if you save any money this way.
6) I do not work for UPS or any of the other branded carriers, just an insider.
7) Express service with UPS includes the clearance, Standard and Expedited does not. Duty and taxes will almost always incur an advance fee as well.
8) There is a cost to transport the parcel back to the shipper. Wy shouldnt they charge for the return? Again, commercial operators are not subsidized by tax payers so they shouldnt be expected to compete with the post office.
9) Canada Post is a majority shareholder of Purolator.
10) UPS does not use its own aircraft in Canada. In Canada, most couriers use Cargojet for their overnight air transport.
http://www.cargojet.com/. I realize this has nothing to do with imports from the USA, but most people will have never heard of Cargojet. UPS and DHL are major clients, basically meaning in Canada with the exception of Puro and FDX, almost all parcels are on the same aircraft to Toronto no matter who you pay (as an example).
11) Unless the shipper checks off "adult signature required" (at an additional cost), UPS is authorized to leave your parcel in a safe place without an signature. They claim it is for the customers convienience, but I think it is crap. A signature should be part of the service and the leaving it at the door should be at the clients request, not the other way around.
12) Did I forgot to cover any points? Feel free to ask me how the Canadian transportation business works.