For a routing like India–US–Toronto, where you're only connecting through a US airport and not formally entering the US, group members indicated that holding a valid US B1/B2 visitor visa is generally sufficient to book and take that itinerary — a separate transit visa typically isn't required on top of it.
Caveats worth double-checking before booking:
- This depends on your nationality and the specific US airport/connection type. Confirm on the current US Customs and Border Protection (CBP) and US embassy guidance for your passport country, since transit rules can differ by nationality.
- COVID-era testing requirements mentioned in this thread are historical — check the current entry requirements for the US at the time of your travel, since these have changed substantially since the pandemic.
- When in doubt, confirm directly with your airline at ticketing, since they enforce transit document requirements at check-in and will flag any missing document before you fly.