Whenever you're trying to ship something internationally, it's just always going to be a little more complicated than just shipping within a single country. There are always a few additional fees, and usually, a lot more paperwork that has to be filled out. However, the smooth operation of international trade relies largely on documentation. This allows governments to track seamlessly what is flowing in and out of their countries, and to make sure that all fees are being paid and all regulations adhered to. That is why you have a little more paperwork to worry about when shipping to Canada with your messenger WI company, rather than if you were just shipping to Oregon.
Some of the paperwork that has to be sent with every international shipment needs to be prepared by you. Other parts of it need to be prepared by your courier company, and sometimes certain forms will require both parties participation. The one thing that you can prepare, and must prepare, on your own, is the commercial invoice. This must go with ever shipment, no matter how small, including small personal purchases made on eBay for example.
The courier company must in turn provide a BOL. This means bill of lading, and it is the most important document which contains the details of the actual physical movement of the goods. Dates and addresses for both origin and destination will be provided so that the customs agents know exactly what movements the goods will have gone through.
Additional documentation is going to depend largely on the types of goods that you're shipping. A BOL and commercial invoice might be enough for small and simple shipments, but when you start getting into larger and more valuable shipments, the matter becomes more complex.
Certain shipments of goods are going to fall under the jurisdiction of international trade agreements, such as NAFTA. When this is the case, you need additional paperwork in order to move your goods. In the example of NAFTA, you need a permit showing that you are allowed to move goods under the terms of that trade agreement.
These are the types of things that can be difficult to track, especially if you're new to international shipping. Making sure that you're doing business with an experienced courier can make all the difference in the world. They can advise you on what documents you must have for each shipment to make sure that you never have anything held up at a border.