Thanks for the detailed reply.These are stages your PR card application go through when linked to your IRCC GCKey account.
Most people receive two ghost updates on their account (status changes from submitted to profile updated) before they receive the final email from IRCC stating that their application has been received/PR card mailed.
GU1: is the first update when the final decision changes to a specific date but states that the application is still in process (this is usually the day your application is finalized)
GU2: is when eligibility review is completed and final decision changes to approved. This is usually the date your card is mailed.
After GU2 you receive an email usually within a day or two saying your application status has been updated and when you log in you can see a message stating the card has been mailed as well as the expiry date (usually 5 years from your approval date).
When can we link the PR card application to gc key , is it after the photo approval ..?