As of July 1st, 2020, the Canada-United States-Mexico Agreement (CUSMA) will take the place of NAFTA. Some shipments that cross the borders of these countries may require special import forms.
At this time, ShipStation does not print these forms or provide a way to electronically upload them. If you require a CUSMA form for your international shipment, you will need to create it outside of ShipStation and include a physical copy of the form with the parcel.
For CUSMA details, go to the Government of Canada CUSMA page. For NAFTA details and forms, go to the NAFTA Rules of Origin help page.