The below steps helped me link my App on the same day my Sponsor got approved. Hopefully it will also work for you. You must use the PA's details to link to MyCIC.
1. Logged in with GC Key account.
2. Permanent Residence > Family Class (Spouses)
2-a. Application Number and Family Name - Copy/pasted application number from email (including the F) and entered PA's last name.
3. City of Birth - I entered 1 space (hit spacebar once)
4. Country of Birth - Selected PA's country of birth
5. Passport Info - Did not enter any passport info
6. Other Application Info - Filled out the other application info as per our application and put '2' as the number of members in the application. I am sponsoring my husband, no dependents.
Again, for 2-a, I selected Family Name, Given Name, Birthday (This is Principal Applicant's (PA) info).
On no. 6, I entered '4' because I have 2 dependents.
Good luck.
Thankyou very much for your help. Now I am going to try.