Upvote:0
I think you got it backwards. On the US-to-India trip, you will need to pass through Canadian immigration when you transit Canada; on the other hand, on the India-to-US trip, you will not need to pass through Canadian immigration (you directly go through US immigration preclearance in Canada). So you would be more likely to run into problems not having a Canadian visa on the US-to-India direction than on the India-to-US direction.
Regardless, Canadian rules officially require a visa for you to transit in both directions. (Even though you won't interact with Canadian immigration on the return trip, Canadian rules still say you must have a Canadian visa.) And airlines are supposed to enforce these rules, so they may deny you boarding on either direction if you don't have a Canadian visa.
Upvote:1
I called the immigration for Canada. I asked them whether I need a transit visa if I am not changing terminal. They answered I needed the transit or visitor visa no matter what.
Upvote:3
A transit visa is required if you are connecting in Canada to an international destination from the US, unless you're eligible for a visa waiver. Indian citizens are not.
Are you a permanent resident of the US (a green card holder)? If so, you may apply for an Electronic Travel Authorization (eTA) from the Government of Canada, which is approved in several minutes in most cases.
If you are not a permanent resident of the US, a normal visitor visa (which is what a transit visa is) application made within the US will take 42-52 days to process.