Yes, you can absolutely use your Suica card in Osaka and throughout the Kansai region. Thanks to Japan's nationwide "Mutual Use" agreement for IC cards, Suica is fully compatible with the readers used by JR West (ICOCA area), the Osaka Metro, and local buses. You can also use it at convenience stores and vending machines in Osaka just as you would in Tokyo. The only catch is that you cannot use it to travel "between" regions; for example, you cannot tap in at a station in Tokyo and tap out at a station in Osaka. You must use a separate ticket or a Shinkansen booking for the inter-city travel itself. Once you are within the city limits of Osaka, your Suica will handle all your local transport needs seamlessly. Just ensure you have enough balance, as you can only "top up" a Suica at JR East machines or at 7-Eleven ATMs.