I think if you enter Canada on your 2nd passport, you must show it at the time you apply to renew your PR card. Otherwise, they will ask how did you enter Canada because they have no record of that. However, if you don't want to show it, I am sure you can think of something else to show as proof when you arrived in Canada. Go and apply for health care and open a bank account. I am sure you will be given some paperwork with a date on it. Keep that in order to show it later.
The land border doesn't always stamp passports, that's true. Especially US passports.
The land border doesn't always stamp passports, that's true. Especially US passports.