Do you have a UPS account (and by extension, a UPS rep)? UPS can act as your broker for shipments into Canada, but you need to setup an account with them and give them authorization to act on your behalf. If you have a rep, the easiest way will be to contact that person and ask for their assistance in putting you in contact with the right department and getting you the forms you will need to fill out. If you don’t have a rep, search UPS for something like “importing to Canada” (your Canada FBA account is importing goods into Canada) and go from there. UPS is very familiar with shipping to Amazon FCs in Canada, so once you are set up things will go smoothly and you can ship to Canada as you run low on inventory.

From Amazon’s Seller Help Hub:

Shipping your FBA products to Canada:

https://sellercentral.amazon.com/learn/courses?ref_=selleru_athena&courseId=593a7f03-ae01-483e-bb32-60c072c1df42&moduleId=915791db-c5a1-4c02-ad04-d0c8a4b0211f&modLanguage=English&contentType=VIDEO&category=TUTORIAL&videoPlayer=youtube

Are you setup to do business in Canada? Is your product allowed to be sold in Canada? Is it labeled and tested to comply with all the rules and laws of that country?