There is no good substitute for keeping complete records. Each PR has what no one else in the world, person or organization, has, and that is the opportunity to keep a complete and accurate record of every border crossing. The PR is the one individual in the whole world who is there each and every time.
And of course IRCC is fully cognizant of this. And, indeed, this is part (just part) of the explanation for why the burden is on the PR, whether attendant a PR RO compliance examination or in applying for citizenship, to completely and accurately report travel history.
IRCC and CBSA have a number of tools to check the completeness and accuracy of what a PR reports. The tools include CBSA history of entries into Canada, access to U.S. records of entries into the U.S. (for non-U.S. citizens, probably even citizens in the near future), and various other sources of corroborating information. BUT in most cases IRCC relies on the PR's report so long as all that other information does not reveal omissions or inaccuracies, and that is what IRCC is ordinarily looking to that other information for, to see whether something shows the PR has failed to accurately and completely declare all travel.
Which is NOT to say that IRCC will unreasonably ignore obvious evidence and indications of presence for periods of time the PR's reporting is sketchy or incomplete. IRCC will exercise its discretion to make reasonable inferences from what is known. Thus, for example, an unusually large number of border crossing events, readily confirmed by CBSA or U.S. records, tends to show the individual is indeed in Canada a lot, and in conjunction with a baseline of information tending to otherwise indicate a life in Canada, that can make it easy for IRCC to conclude the PR was in Canada for well over the minimum 730 days in five years to meet the RO even though the PR's submissions may have lacked the level of detail requested AND, it should be noted, USUALLY required at least within a fairly close range.
Nonetheless, if you really provided little or no actual travel date history, it is quite remarkable and, I would GUESS very lucky, that your application did not end up in non-routine processing and incur a lengthy processing timeline delay.
My guess is the risk of NOT being so lucky in a citizenship application is high.
That said, some estimating of dates, with explanation, is probably OK in a citizenship application . . . even though it appears IRCC has dropped (I could not find it again recently) its previous FAQ advice that applicants could "estimate" travel history in their citizenship application, so long as they clearly indicated which travel dates are estimated. Obviously, estimating travel history undoubtedly increases the risk of non-routine processing and a much longer timeline. And the more travel history is estimated the greater the risk.
Lowest risk is completely declaring all dates of travel and doing so accurately.
Of course there is a more strict approach to assessing presence in the citizenship application process, given the nature of the status and its lifetime duration, and given that the number of required presence is another full year of days.
Obviously multiple crossings in the same day are no big deal since it is just the day that is reported. (That would involve lots of practice sitting idly in queue I'd expect, so you should be well prepared for the citizenship application process-crawl. I cross the U.S. border way, way less often than I did in the past, perhaps largely due to the social and political environment in that S*hole country, but at least in significant part due to the lines, just the traffic alone let alone the potential examinations.)
In the citizenship forum there are various discussions about how to reconstruct travel history if the prospective applicant has incomplete records. The caution is to be sure to advise or explain this to IRCC; that is, to acknowledge some estimating derived from reconstructing the history as well as one can.
Ordinarily long haul truckers should have logs which would be a huge help in reconstructing the travel history. Others in the forum are more familiar with procedures to obtain U.S. records or CBSA travel history, which will usually fill in most of the gaps (for many, all the gaps, but not for everyone, so you should not rely entirely on this information). For someone who was crossing the border regularly for work, just looking at the work history should help identify much if not most of the travel history. For example, if I knew I was making deliveries in the U.S. five days a week most weeks from March 2016 to June 2018, it would be easy to identify most holidays and remember longer periods of time off, and just use the calendar to identify the vast majority of dates for that two plus year time period.
Trips to the U.S. do not even count as a day absent unless the PR spends two or more consecutive nights in the U.S. (Leaving one day and returning to Canada the next results in ZERO days absence, since the PR is actually physically present in Canada any day the individual is leaving Canada and any day the individual returns to Canada.) Technically all day trips need to be declared. This could be tedious. But tedious is not impossible. Not even impractical.
How much IRCC lets slide varies greatly. There tends to be a good deal of flexibility exercised relative to the PR RO, especially when it is well apparent the PR is well settled and actually living in Canada. Some similar flexibility, but less, is also exercised in citizenship application processing. But as I noted before, the best approach is to follow the rules and give IRCC direct answers for its requests. As best one reasonably can anyway.
