I don't know about shipping packages from Canada, but shipping from the US to any foreign country is a PITA (at least for an average civilian). First, you have to find the right customs form to fill out in quadruplicate. There are different forms depending on the size and weight of what you're shipping and what shipping service you're using. (For example, the USPS Priority Mail International Flat Rate Medium and Large boxes require a different form than the Priority Mail International Flat Rate Small boxes.) If you're using any shipper other than the USPS, such as UPS or FedEx, you have to include a commercial invoice code identifying the category of product you're shipping and its country of origin (where the product was manufactured). And if you're using FedEx or UPS, there's a chance that the delivery service may neglect to collect import duties when they deliver the product to the recipient, later billing you the sender for those duties. I've had this happen to me on two separate occasions when shipping from the US to Canada, requiring me to spend many hours tracking down the recipient to get reimbursed.
I wish it was as easy as "What's inside?", "Sign here"...