Upvote:7
To add to phoog's answer, if you are both flying into and out of Terminal 1 in Toronto during business hours on the same day, transferring from International to the US, you will go to directly to US immigration, without going through Canadian immigration. (If you will go through Terminal 3 or need to transfer between terminals, then you will need to go through Canadian immigration first and then go through US immigration.)
However, even if you might not go through Canadian immigration, Canada's rules still say that you are required to have a visa to transit Canada, since you do not qualify for the Transit Without Visa programs. The airline is supposed to make sure you meet these requirements before letting you board.
Upvote:9
You will pre-clear US customs in Toronto, but that does not exempt you from needing a transit visa. There is a Transit Without Visa program that does not apply to you because it is only available to citizens of Indonesia, Philippines, Thailand, and Taiwan. There is also a China Transit Program that is available only to those holding a passport from the People's Republic of China.
As an Indian Citizen, you can find out about your visa requirements using the visa tool. It will lead you to a page describing transit visas, which describes how you can apply online or with a paper application. The next page says that if you choose to apply with a paper application, you must
Select the country/territory you will be applying from to find out where to submit your application. You can choose your country of nationality or the country/territory where you have been legally admitted.
Therefore, if you choose to submit a paper application, you can apply in Delhi.
Canadian transit visas are free of charge, but if you submit a paper application, you will have to do that through a third-party service provider, which will charge a processing fee.