Your assessment is wrong. the OP will face problems with the airline, and not at the border.
1, the airline won't know that the OP is a PR or not, but they will scan the passport which is checked for an eTA. As a PR, the OP technically cannot have an eTA and the system should then issue a "do not board" response. The airline will then have to ask for a valid visa, or other document (i.e. PRTD or PR Card) which would allow the airline to bypass the "do not board" remark in the system. The airlines face heavy fines for transporting passengers to Canada who do not have the proper documentation.
2. The CBSA at the port of entry will not care about how the OP got to the inspection point. Their job is to make sure they verify identity and determine admissibility; and to do this they can run any number of checks. Even without a CoPR, officers at the border can run background checks and match records to verify PR status.
