Fellow Montrealer here with same frustration. I started a
thread in Apple's forums about this. I also
filed a bug request about it, I encourage you to do so.
If bringing back the "General -> Language & Region -> Region Formats: Advanced" option is too complicated, simply adding a "Québec" or "French Canada" as a region with the appropriate date, number and currency settings (see below) would fix the issue.
English Canada / French Canada
Tuesday, September 13, 2016 / Mardi 13 septembre 2016
$1,234.56 / 1 234,56$
4,567.89 / 4 567,89
3:45 pm / 15:45
Right now, there is only one "Canada" choice in the list of regions and it follows the English Canada standards. There needs to be two regions, not one.