I have never once been checked for Yellow Fever in either India or Canada when arriving on the Ethiopian Airlines flight.

Officially, India requires it even if just transiting at Addis Ababa, so the duration of the stop and whether you stay at the airport is irrelevant.

Canada has no official policy on the matter - if you are deemed to be at risk you may be asked for your vaccination and quarantied if you don't have it - but there is no specific threshold.