I'm pretty sure Montreal really doesn't care about it's 3 km radius population numbers, nor should it.
This really isn't a competition but just another way of viewing statistical information that's more consistent across cities. The 3 km radius for most cities accounts for the variables, although it's not the best for Montrela, Toronto and perhaps Vancouver - in those cases the 8 km radius might make more sense.
I would say it's more informative than the actual 2021 Stats Canada downtown population numbers, which experts devised yet people pick apart for inconsistencies. For example I would take the radius numbers as a more meaningful indicator of core population vs. these downtown numbers (but
yes, those are two different things):
scroll to see the table
Downtown 2021 Population
Halifax - 20,267
Calgary - 38,663
Victoria - 40,681
Winnipeg - 42,394
Edmonton - 55,997
Ottawa - 62,725
Montreal - 88,169
Vancouver - 113,516
Toronto - 237,698
Again measuring different things, but in terms of core population I prefer radius.
Cities are different, that's cool and awesome. The fact that some will be less populated within a defined area due to geography is a fact. Doesn't make that city better or worse. Some people will prefer a largely uninterrupted land area for urban exploring while others will enjoy the breaks mountains and water provide. Larger cities will also have infrastructure that doesn't hold population such as the rail lines into Toronto, but they enable a large number of people to enter the city
Really not a competition folks, just another way of understanding cities.