Normally Canadian officials are tolerant of obvious mistakes but unfortunately (that is for the offender) there has been great concern over the number of restricted weapons flooding in from the United States into Canada. That may compel prosecution. It almost certainly would at Pearson in Ontario where the gun import issue is most acute but perhaps not elsewhere. All the cases I have dealt with before involved guns carried in by car, when the weapons are always confiscated and an on the spot judgement made on further action. I cannot judge what the position will be in this case