USPS and Canada Post were the most cost-effective way to deal with customs for the longest time. Unsure if that's the case anymore.
[1]: https://www.cbsa-asfc.gc.ca/import/courier/lvs-efv/menu-eng....
In a perfect world, we would just outlaw brokerage fees, and just have CBSA do the clearance since all of the information is already input in a computer system. We should at least outlaw forced brokerage. I never agreed to have UPS act as my agent, so I get pretty upset when they charge me a fee no one agreed to.