Once you obtain Canadian citizenship, Canadian passport can be applied from the Canadian embassies/consulate/high commissions overseas
After that you have to surrender your Indian citizenship and cancel your Indian passport. This can be done in India i believe through the regional passport office.
Around the same time you have to get an Entry Visa (called X) which is provided to former Indian citizen. I am not sure which entity you have to apply for this Entry Visa from in India
Only after completing 6 months living in India on this entry visa, you will be eligible to apply for OCI within India
Try and follow some posts
@nivaan5 . His case was a little different than yours as he applied for citizenship in Canada and obtained his passport in Canada. After that he travelled to India using his Indian passport (since there is a grace period of 3 months within which you can use the Indian passport). But then he surrender his Indian citizenship and cancelled the Indian passport in India
https://ociservices.gov.in/
Foreign nationals cannot apply for OCI in India while on Tourist Visa, Missionary Visa and Mountaineering Visa. Moreover, the foreigner has to be ordinarily resident of India to be eligible to apply for OCI registration in India.
Note: 'ordinarily resident' will mean a person staying in a particular country or in India for a continuous period of 6 months.