Thanks for posting in the Community, @ssmass-marketing. I've got the details you need to help achieve your goal.
In QuickBooks Online (QBO), you're able to assign a multi-GST supplier in a single expense ledger account only. Just choose the Default expense account in the Supplier Information window. View the screenshot below for your reference.
I recommend running the Account QuickReport of the ledger account you use for your multi-GST supplier. It helps you view all its associated transactions within a specific period. Just click Run report under the Action column in the Chart of Accounts menu (see the screenshot below).
Lastly, you can visit our resource hubs below to learn more about effectively managing your suppliers and GST in QBO: