TurboTax downloading from CRA's Auto-Fill My Return service when you sign into your My Account from inside TurboTax.
When you sign in from in TurboTax, TurboTax enters your SIN number into the window for you. All you need to do is enter your My Account sign-in credentials and then TurboTax takes over.
https://turbotax.community.intuit.ca/replies/2994684
