Similar experience in 1994 with our group in I-Falls.  4 of us were hauled downstairs, placed in separate rooms with a stainless steel bench and instructed to place everything but our skivvies in the plastic box outside the door.  No one ever questioned me but 2 of the guys were grilled.  About an hour later someone kicked the box of clothing back into my room and said "Get dressed!"  We all got back up to the parking lot and the Chevy Blazer was emptied on the asphalt; packs, canoe un-done, floor mats, glove box contents, etc...  If it wasn't nailed down in the car it was on the ground.  As a participation gift, the German Shepherd kindly pissed on the rear tire.

Back then I don't think they cared whether or not you were a US citizen.  They were just looking for the good Canadian Pharmacy.  ;)