1. When CIC stamps my visa & couriers it back to my indian address, how to get back my passport to Canada?
2. Can I ask an authorised person to get my passport to Canada from India?
Whoever is at your Indian address can arrange for someone traveling from India to Canada to bring the passport back for you - that is, get it back the same way you got it to India.
I know you are not supposed to send Indian passports by mail outside of the country, but could whoever gets your passport at your Indian address perhaps send it by courier to you in Canada? See if others have had no problem doing this first, though.
3. Will CIC at new delhi question me that if I am currently in Canada how did I send my passport to New Delhi? Will it cause any trouble to my application?
CIC will most likely not care - it is an Indian law, not a Canadian one. If they do ask, just tell them you had a friend take it to India for you.