Are you asking about the consequences for making a misrepresentation to CBSA officers in the process of applying for entry into Canada?
Or are you asking what is the probability that a returning PR long in breach of the PR Residency Obligation will get caught making a misrepresentation to CBSA officers in the process of applying for entry into Canada?
Of course the difference is huge. Many, many people at least fudge some answers at a PoE without triggering formal misrepresentation proceedings. What many of those who think they got away with it likely overlook is that even if the examining officer does not overtly confront the traveler about making a misrepresentation, the officers recognize and perceive evasive and outright deceptive answers many if not most times, and that perception or suspicion influences how things go . . . again, even though the border official does not explicitly address the issue of misrepresentation.
Moreover, in terms of the odds, it is readily apparent that as soon as the client number is entered (via keyboard or document swipe), that pulls up the traveler's records on the officer's monitor, and the officer has access to a range of information which will help the officer evaluate the traveler's answers to questions, including answers about previous time in Canada. At the PIL (primary inspection line) this is what can trigger a referral to Secondary, and in Secondary the examining officer can and is more likely to access the records more extensively. The scope of information readily accessed has steadily increased over the years, and the technology has enabled officers to access the information more quickly. All of which is to say that whatever the chances of getting away with lying at the PoE were in the past, the odds of getting caught are increasing . . . and of course the bigger the discrepancy, the more likely an officer will spot it and the more likely it will trigger negative action.
As for the consequences, there is a huge range what can happen due to making a misrepresentation at the PoE. As already noted, officers might not even verbally address it let alone focus on it, BUT it could still influence their decision-making and what happens next. Actual impact can range from triggering more questions to resulting in a perception of deception having a negative impact on the traveler's credibility which in turn negatively influences the decision-making, or the misrepresentation could trigger a formal investigation the result of which can range from simply a black-mark on the traveler's record to full blown criminal prosecution and deportation proceedings (actual deportation to take effect after a sojourn in secured public housing, the kind of housing with bars on the windows but not many windows). The latter, the more extreme consequence, does not appear to happen often. Past examples in which there was full blown prosecution, including criminal charges and loss of PR status, include cases involving more obviously intentional efforts to deceive, such as PRs who have entered forged/fake stamps in their passport to make it appear they exited and returned to a country where they were living abroad, so they could refer to those stamps as times they traveled to and stayed in Canada.
Overall, in general, it is likely that in the last decade Canada has investigated and taken action in more immigration related fraud cases each year than it did in an entire decade previously. That is, interdiction, investigation, and enforcement are all way up from how it was in the not so distant past.