Choose where to begin based on your business’s specific situation, taking into consideration your product category, distribution rights, resources, and other factors. Many selling partners have successfully launched immediately across all of Amazon’s North American stores. Amazon tools and services, like Build International Listings (BIL) and Fulfilment by Amazon (FBA) services in North America, make selling across all North American stores much simpler.
Of course, if you’re not comfortable selling across all 3 Amazon services yet, or if your distribution rights don’t cover all stores, you can start with one or two of them.
With a North America Unified Account, you can conveniently switch in Seller Central between Amazon.com, Amazon.ca, and Amazon.com.mx selling partner tools to list products and manage orders in multiple stores. You have the option to list in one, two, or all three of the available North American services. When managing your Amazon inventory across Amazon's United States, Canada, and Mexico stores, it is important to understand the difference between the Global SKU and the store-specific SKU in Seller Central. You can find more information on these topics here