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](http://www.cic.gc.ca/english/department/twov/travellers.asp) 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](http://www.cic.gc.ca/english/department/ctp/eligibility.asp) 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](http://www.cic.gc.ca/english/visit/visas.asp).  It will lead you to [a page describing transit visas](http://www.cic.gc.ca/english/visit/transit-apply-who.asp?lnktrk=visa_transit_air), which describes how you can apply online or with a paper application.  The [next page](http://www.cic.gc.ca/english/visit/transit-apply-how.asp) 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.