If really concerned I guess you could always go through separate immigration lines when you return as no reason to go through the same line unless you present a single arrival card that is.
Depends how much assistance you think your husband needs to present his COPR, answer a few questions , hand over a Canadian address for his PR card and pass through customs.
But as Zardoz says if you are making the trip post COPR issue, and in unlikely event can show if asked your proof of recent outward journey such as a boarding pass stub or itinerary then should not be a problem.
All too easy to over think things