On one hand you are in an enviable position relative to most PRs who have failed to comply with the PR RO but who now want to retain PR status: the frequency of your trips to and from Canada, combined with a visa-exempt passport, indicate good odds you can again travel to Canada without incident. You have been through the process recently. You basically know the drill, at the airport and at the PoE. If your next trip follows that same script, and is prior to the end of the leniency period, odds are good you are allowed to board the flight and that upon arrival at the PoE in Canada the screening will be very similar to what you experienced the last couple times.
If you follow the same script, and thus come to visit, and after discussing things with your parents in Canada or thinking things through, it should be no problem to change your mind and stay, and have things shipped from the UK to you.
But of course you are indeed a PR who has not complied with the PR Residency Obligation, so upon arrival at the PoE you are subject to being reported for inadmissibility. This does not seem likely to happen unless there is something different about the trip which causes a PoE officer to have suspicions. Given the frequency of your trips, it is hard to imagine this happening unless the screening officer apprehends that you are indeed coming to Canada to stay. Or, are staying in Canada and your trips are visits abroad. Or, there is something about you that otherwise raises suspicion . . . like suddenly coming via the U.S. when that has not been how you traveled to Canada previously.
Overtly lying at the PoE is, of course, a bad idea.
On the other hand, since you could be subject to losing your PR status at any time, on any trip, it is probably a bad idea to just count on making the trip again and having your stuff shipped to you later. Probably better to plan to visit again, maybe gather your stuff before leaving and arrange for someone to ship them to you IF during this visit to Canada you decide to stay. That is, be prepared for things going in either direction, planning to visit so you can better make up your mind about coming to live in Canada, but also being prepared to stay if that is how things work out.
By the way, the getting off and staying during a layover for a connecting flight, especially one to a destination that really is out of character for you and your traveling history, is a really bad idea. If recognized, which it quite likely would be, it would be an obvious ruse, an obvious attempt to game the system, and could get you banned from Canada for five years.
In any event, if your travel is much like before, your odds are good. If you travel the end of June or in July say, for just another visit to family, no need to misrepresent anything about when you were last in Canada or for how long, odds are very good it will go smoothly.
Of course there is a risk otherwise. IRCC and CBSA could implement changes regarding visa-exempt PRs which shut down that way of getting abroad a flight without a PR card anytime, without notice, regardless the leniency period (there is no guarantee the PR rule will not be enforced). That would require you to go via the U.S. and going via the U.S. might result in elevated scrutiny at the PoE.
Or the next time there could be elevated scrutiny at the PoE anyway.
As long as you make it to a PoE, which you can do via the U.S. if push came to shove, if there is a residency examination and the officials challenge you about PR status, you can either surrender PR status then and will most likely be allowed to enter as a Foreign National visitor, or you can accept being reported for being in breach of the PR RO and will be allowed to enter Canada . . . at which point you have less than a month to decide whether to appeal, which will allow you to stay pending the appeal, or you could allow the Removal Order to become enforceable and then pursue an Express Entry application. But you might want to consult with a lawyer about H&C arguments based on the extent of time you have been in Canada, the fact of your parents living in Canada (if I recall correctly, that they are in Canada), and putting reasons for time away in the best light possible. Recently saw a case in which an appeal did not even reach the IAD for three years, and while living in Canada after being reported does not count toward the calculation of days in Canada toward meeting the PR RO, they can be a significant factor in the H&C assessment.
You are in a much, much better position than the vast majority of PRs who have not complied with the PR RO but who want to now retain PR status. The odds are in your favour. But since you are in breach of the PR RO, of course there are no guarantees.
Caveat: Much of the above is assuming there was nothing in how things went when you last entered Canada, or the time before that, which has caused you to apprehend it might not go so smoothly the next time. You are the one who has the most experience of anyone here regarding using a visa-exempt passport to fly to Canada since March 16, 2016. You have as much information about how that goes as anyone.
But again there is no guarantee it will go as easy the next time. As I often emphasize, how it has gone even ten or twenty times does not necessarily dictate how it will go the next time. I have personal experience seeing different outcomes relative to both boarding flights (yeah, I have personally experienced not being allowed to board a flight at the last minute, there at the gate, and can only imagine the frustration of other passengers given the flight's delay while the airport personnel had to go into the plane's hold to find and remove my suitcase before the plane could take off) and PoE encounters, even though the essential circumstances are very much the same as they were many times before. I have personal experience in observing how just one small difference in detail, an apparently insignificant difference in detail, can trigger a very different encounter at a PoE. Those who extrapolate and offer advice as to how things will go based on two or five instances drive me crazy; dozens of instances is no assurance about how things will go the next time. And this is especially so in reference to the prospect the applicable rules will not be enforced. No matter how often the rules have not been enforced, there is always a substantial risk the rules will be enforced the next time, if only because that is supposed to be what happens.
