Depends what exactly you want to add. Not having AC myself. But let's assume you want to have Canada in some DDay scn, you have to set this in the editor, so need to change the scenario in question.
There you can:
- place Canadian units on the map
- enable Canada as nation, and set up its side (tho should default to allied)
Then save the scn, but it's surely better to backup the original elsewhere before (unless you want to reinstall in case you want to go back).
Also, if you want to add Canadian units to your own core throughout the campaign (like In AC with US/UK), you need to make further changes. IIRC that can be done by adding the nations numerical code into the campaign file under "nations" , seperated by comma if you have more than one country.
Example:
# This file contains Panzer Corps campaign structure
FormatVersion 1
# Entry points
# Name Label in campaign path Description Side Nation Starting prestige Display name
D-Day 20 IDS_CAMPAIGN_DESCRIPTION_AC6 1 1,2 8000 IDS_CAMPAIGN_NAME_AC6
The numbers 1, 2 are for UK and US here. Do something similar for countries you want, but make sure the tabs between columns remain intact. Again backups are recommended of course.
-