here is official statement ---
https://www.canada.ca/en/immigration-refugees-citizenship/services/coronavirus-special-measures.html?fbclid=IwAR0WOumUWf1EPak_J4dTkhMlxdiTthOlqTU_26aaMMqnH5ycRdgmiSA6_ss
If your permanent residence application has been approved, but you
can't travel to Canada before your documents expire, use the
web form to tell us why you can’t travel.
Once it’s possible for you to travel, use the
web form to let us know. We’ll then give you more detailed instructions regarding restarting the processing of your permanent residence application.
Landing appointments will be held by telephone Latest update: March 15, 2020
Starting March 16, 2020, we’re cancelling all in-person permanent resident landing appointments until April 13, 2020.
If you had a landing appointment already booked, it will be
held by telephone.
We’ll contact you by email to let you know when your phone appointment will be. Use the
web form if you need to update your contact information.
If your confirmation of permanent residence has already expired
Use the
web form to explain why you
couldn’t travel.
Once it’s possible for you to travel, use the
web form to let us know. We’ll then give you more detailed instructions regarding restarting the processing of your permanent residence application.
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from above I am not seeing they are not allowed to travel to Canada, once they got approved.