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!

Here's the link to connection information at YYZ from International to USA:-

http://www.gtaa.com/en/travellers/co...nnection_tips/

It depends on which terminal your parents will be arriving and departing. AFAIK but may not be up to date:-

T3 to T3, T3 to T1 and T1 to T3 - Must clear Canadian immigration and custom/excise (CBSA).

T1 to T1 - "simplified" CBSA.

For most airlines, passengers will pre-clear US immigration and custom/excise formalities in YYZ. (i.e., not on arrival in US)

What airline will they be arriving and departing?

sounds like your parents will be flying delta and continental...if so then they will only go through terminal 3. im not sure if you can get a visa on the spot from yyz, you might, lots of countries will give you a visa on the spot...