Choose where to start based on your company's specific situation, always taking into account product group, distribution rights, resources and other factors. Many Selling Partners have successfully started selling in all Amazon North American marketplaces at once. Amazon tools and services, such as Build International Listings (BIL) and FBA services in North America, make it easy to sell across all the North American marketplaces.
If you don't feel ready to sell on all three marketplaces yet or if your distribution rights don't cover them all, you can start with just one or two of them.
A North American unified account allows you to easily switch between Amazon.com, Amazon.ca or Amazon.com.mx seller tools in Seller Central, to list your products and manage orders on multiple marketplaces. You can decide whether to list on one, two or all three available North American marketplaces. When managing your Amazon inventory on Amazon's US, Canadian and Mexican marketplaces, it's important that you understand the difference between the global SKU and the marketplace-specific SKU in Seller Central. You can learn more about these topics here