My main to reason to do instructor course is to get job in Canada in order to build my hours.
The problem is that you already have a foreign CPL. Doing just a CFI course in Canada will not qualify you for a flight instructing work permit because the course length is too short (less than 8 months).
You could possibly ask a school to put together a custom course for you (more than just a CFI course) that's over 8 months in length, although obviously that will be a lot more costly.