Originally Posted by
pitz
No, because if one is denied entry to the USA by CBP, then one is ejected back into Canada, and will be required to immediately report to Canada Customs.
A passenger will not be allowed to board the aircraft overseas, destined to Canada, if one is known to be inadmissable to Canada for any reason. Even if they have an onward connection to a country where they are admissable.
Good point. That is part of the preclearance process: you are inadmissible to the US you then have to go straight to Canada Customs (even if you just entered from the curb!). I guess in the reverse situation mentioned (intl-transborder) they save you from Canada Customs since you are going right into preclearance.