If your route to Canada includes a layover at a US airport (e.g., flying India → Dubai → Seattle → Vancouver) with a different operator handling the final leg:
- Airlines will not let you board the US-bound flight without a valid US visa — a short connection time doesn't exempt you from this requirement.
- You need either a US C1 transit visa or a B1/B2 visitor visa to be permitted to transit through a US airport under this itinerary; a 4-hour layover does not change that requirement.
If your routing involves any US stopover, secure the appropriate US visa well before booking — don't assume a short or same-day connection avoids the need for one.