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 marketplaces much simpler.
Of course, if you’re not comfortable selling across all 3 marketplaces yet, or if your distribution rights don’t cover all marketplaces, 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 marketplaces. You have the option to list in one, two, or all three of the available North American marketplaces. When managing your Amazon inventory across Amazon's United States, Canada, and Mexico marketplaces, it is important to understand the difference between the Global SKU and the marketplace-specific SKU in Seller Central. You can find more information on these topics here