The CARS spell it out. You will first need a commercial/ATPL licence - again spelled out in the CARS. Just be warned - Canada has no Bi-Lateral agreements, so credit for past experience towards reducing the hours required towards the instructors may not necessarily be awarded.
If you have the requirements for ATPL, you go straight to ATPL (ie don't need a commercial first) and then you get 50% credit towards the time required for the instructors.
I had a S African instructors - the syllabus is quite different, and the standard it MUCH higher! With an ATPL, I still won't complete the instructors in the min time allowed.
Hope this helps