CBSA's mandate and priorities are pretty clear: first and foremost national security and public safety, while 'facilitating' free flow of persons and goods acc to Canadian law. Or stated as a mission, "To ensure the security and prosperity of Canada by managing the access of people and goods to and from Canada."
What this means in practice is that there is always some trade-off between resources available and the potential benefit. Or, put differently, some combination of judgment by the officers based on potential costs and benefits balanced against priorities. And yes, sometimes inconsistency - after all, they do random searches sometimes, which is nothing if not inconsistent (although perhaps reliably or predictably inconsistent). Within the immigration/border crossing tasks, there is a certainly recognition that no system of border control in Canada will ever be 100% successful, and the costs tend to rise exponentially for small improvements, particularly at the land border.
So the way I would look at this case (or in general): does the original poster represent a security risk? Seems unlikely, and an investigation into his residency obligations isn't like to change that much. Will a long and expensive examination and appeals process lead to any benefit to Canada? Seems unlikely, as he and his family seem able to support themselves. Even a process that resulted in deportation/removal would lead to ... well, what exactly? Wife and children settled and he'd probably be successful re-applying for PR status eventually anyway.
So stricter enforcement here: to what end?
It's easy to second-guess the CBSA officers, or think they didn't do what they should have. In this case - whether it was accidental or the part of precise information and careful judgment - it cost the government less with basically the same outcome.
Why don’t you consider the US then?
