Mats, Thanks for your reply.
There are two issues here;
1. One is the expiry of PR card. The reason here to use land crossing is because PR card is expired , so if the US agent at US entry wants to see
the card and it is expired , so it could be a problem.
2. second is , to correctly record arrival departure from US , if one enters US by air then one must leave US by air. Previously US used to have I-94 cards for visitors which you could give to the CBSA land border agent when crossing to Canada but now they have abandoned those for the electronic system.
https://help.cbp.gov/app/answers/detail/a_id/1674/~/report-departure-if-entering-by-air-and-departing-by-land
Correct me if I am missing something.