So I’ve downloaded the 2 ISO’s mentioned, FR-FR and FR-CA, and imported them into a DS with nothing set as the locale. This is a base installation with zero changes made to the TS, CustomSettings or Bootstrap.
As i suspected they both installed as per the languages that the ISO represent so FR-FR installs French and FR-CA installs French Canadian.
From your first post the issue appears to be that the keyboard locale is incorrect, shows as French Multilingual when it should be Canadian French and the inputlocale needs to be French Canada.
IMHO the easiest thing would be to get a French Canadian Windows 10 Installation disk and use that as it appears to install the language and keyboard that you require.
If you really need to use the FR-FR disk then i believe these are the settings that you will require in your customsettings.ini file:
I also think you will need an active internet connection as the install that i completed installed the relevant language packs from windows update.