Hi there members-guru1-ca,
It's important that all your transactions are entered correctly so your books will be well-balanced. QuickBooks Online is a great tool able to connect to various services through third-party apps so that you can streamline the process of entering transactions in your books. I can point you in the right direction to connect Shopify to QuickBooks Online.
As mentioned by 4Gal, a third-party app would be needed to connect Shopify to QuickBooks Online. To see the details of these apps to see if there is an app able to connect two Shopify stores, or if you'd need to use two separate apps to connect the stores, you can go to the Apps section of QuickBooks Online, then search Shopify. You can click on each app to see information by the developer of the app, some reviews from users of the app, as well as contact information for the developers of the app if you have more questions about their software.
If you have any other questions, feel free to reach out here.