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Every crossing between Canada and US requires passing an immigration check by the ICE/TSA authorities. If he takes a train or a plane, the check would be once he lands in USA/arrives at the US spot where he leaves the train.
I am sorry, but "sneaking" into USA from Canada and not being scanned by the authorities is not possible - he can only cross at designated areas, and all said areas have check points for immigration purposes either at the border or at place of final destination (if by plane or train).
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