Others can comment as well but once you get your PR approved and your COPR in hand you need to arrive in Canada within the validity of the COPR to complete the PR immigration formalities.
In your situation what many people do is referred to as a ‘soft landing’ , they complete the initial PR landing, apply for PR card sent to a Canadian address, obtain a SIN , then they return to their home country to tie things up before emigrating permenantly.
It is possible having completed the initial landing to stay away for near 3 years as long as the 2 years out of 5 from initial landing residency is met.
So to answer your question there is no issue with staying on in the US as long you keep in mind the COPR expiry date. Personally if were me I would complete a soft landing to activate my PR as a priority , return to the job in the US and wait out a job becoming available in Canada keeping in mind the residency obligation.
Note that a PR card can only be mailed to a Canadian address so you would need to make arrangements for that to be forwarded to you in the US given once a PR the card is expected to be shown for any travel back to Canada , specifically boarding a plane.