Originally Posted by
tentseller
The answer is yes or no depending on which airline you are flying into YYZ and out of YYZ.
If the transit is wholly *A and in terminal 1 then yes, you do not enter Canada and head to US CBP preclearance. GUWonder's step would apply.
If you are arriving T3 or have outbound at T3 then the CBSA immigration, pickup bag, custom, recheck, US CBP and security are the steps.
That's right, thanks for making that clear.
[The ICN-YYZ flight comes into T3 and is not a Star Alliance flight. The LIM-YYZ flight comes into T1 and is AC. But, as noted above, the onward flight from YYZ can make all the difference too, even in the case of coming into T1.]