My parents (Malaysia passport holder) are coming to visit me in the US. They have US visitor visas (but not green cards).

Their routing is KUL-ICN-ATL-YYZ (one ticket) and then YYZ-CLE-DAY (second ticket). It's a long story how they ended up with this routing, but it is what it is! Ideally they could just fly ATL-DAY (and bypass YYZ and CLE), but that risks a cancellation of the return trip.

They are in Toronto for around 3 hours, don't want to leave the airport, etc. Malaysia is on the list of countries requiring a visa. Is it possible for passengers from an international flight from the US, connecting to another international flight to the US, to bypass Canadian immigration and customs in YYZ?

This takes place on Friday, so no time to apply for a visa.

Thanks very much!