Very surprised to hear that. I know the FO personally who had quite a run in with 4 Alberta judges back in the late 90's when DFO regularly did road blocks and road side checks like you describe. As a result of the challenge and fuss they raised over the search, DoJ advice was that such searches require a warrant - same as a police roadside check, they have no right to search your vehicle unless they have intelligence that a crime has been committed and seizure of evidence is time sensitive ... otherwise they need a warrant.
If you would have said no to the FO's they would have had no recourse. Still, surprised it happened at all as I know DFO abandoned such things for at least a decade or so. I'm gonna contact him and chat. Just saw him the other night at a retirement party.