Hi Meastw1m,
Welcome to Community! With QuickBooks Online Accountant, you'll have the ability to add clients to your books. This enables you to access their accounts directly from your firm, so you can complete the daily bookkeeping tasks within their company. With regards to your clients, they would enter their own Business Number into their account, when they set up their Company in QuickBooks Online. They'll also have the associated Sales Tax rates set up for their province. This enables you to do what you love, while watching your firm grow!
Please don't hesitate to ask other questions. We're here for you and we love to help!