Originally Posted by dkc192

AC will issue your connecting BP at your point of origin and transfer your checked bags automatically in YUL. Upon arrival in YUL, follow the signs for US connections, which will take you to a security checkpoint (just like a regular security checkpoint as if you were departing YUL) before you enter the US preclearance area. CBSA (the Canadian border services agency) may do a cursory check en route, but it won't be as if you were an arriving pax into Canada.