You will get the validity for 5 years for CPL and RT based on canada for your Indian RT Permit. I tried for 5 years. As RT is based on CPL, your canada cpl is life time valid except it has got to be renewed every 5 years for flying and keeping your medical valid.
No, it is useless getting it for 20 years. To get the Indian License is fine, but sit for the first attempt which even my american citizen Indian friend sat and passed it so if he can pass why not all of you and once you do that, then you will get it for life time.