Originally Posted by
Geoflying
In that case you would have had to pick up your bags in YYZ to go through US customs anyway even if checked through to LGA. Nothing says you were obliged to put those bags on the belt again at YYZ.
One no longer picks up bags at YYZ (or YUL or YVR) when doing this type of connection to the US from a domestic flight. Bags remain sterile and you ID them when you go through pre clearance on a TV screen at the immigration officer's booth. So bags must be short-checked to YYZ for pick-up at the regular carousel (same for CC is he has any checked bags).