Upvote:0
If you are not from a visa-exempt country, you will need a transit visa. If you are from China (mainland), Indonesia, Philippines, Thailand, or Taiwan (without personal ID), you may be able to transit without a visa under certain conditions. Seeing that you are travelling to Mumbai, I am assuming you are holding an Indian passport, in which case, yes, you will need a visa.
If you don't have a Canadian visa, changing the itinerary would be the best option!
Upvote:4
You need to be approved for the Canada transit visa and have it stamped on your passport before you are able to transit through Canada. Once you are approved, you will receive instructions on how to submit your passport for stamping, but at this date it's unlikely that you have enough time to receive the visa. I strongly encourage you to change your flight itinerary. You will be denied boarding without the transit visa stamped on your passport.