The Canada thing is because so many businesses use UPS and FEDEX. These companies always always make sure that customs gets involved when shipping between Canada and the US so that they can charge outrageous handling fees. There are a couple of class action lawsuits against at least one of these shippers because of their fees. Always use USPS for Canadian shipments if possible.
I'm happy to pay the customs fees (well not happy, let's say willing). I just am not able to - because of my shipping address.
Please note that while we tend to ship with UPS, we are willing to ship via another courier by request. We have had many requests from Canadian customers to ship via USPS or EMS.