Hello Jobworks,

Welcome to the Community! To make life easier for our customers, Intuit allows users to sign up for both QuickBooks Online and QuickBooks Self-Employed subscriptions using the same email address. I'll explain how to do this so that you can move forward with experiencing all of the great features that QuickBooks Online has to offer. 

When you go to the QuickBooks Canada website and click the Buy Now button under the QuickBooks Online Easy Start plan, you'll be brought to a screen that shows fields for entering an email and password. These fields are only used if you don't already have any subscriptions for QuickBooks Online or Self-Employed. If you enter your email address there, it'll give you the "this email already exists" prompt that you mentioned in your post.

Since you already have an existing account, you'll click on the blue Sign in hyperlink found just above the email address field where it asks Already have an account?. This will allow you to sign in with your existing credentials and continue setting up your new QuickBooks Online Easy Start subscription. 

Please let me know if you have any other questions about this. I'm here to help!