Visible crew/equipment: When the presidential procession is going down a street in the very beginning, on one of the black cars you can see the reflection of the vehicle with the camera crew shooting the movie.
Other: Soon after Dan Ackroyd makes John Candy translate all the phrases spray-painted on the van into French, you can see them driving on the road and all the spray-paint has gone. Then later in the film it reappears and stays for the rest of the film.
Other: Sheriff Bud B. Boomer runs to the top of Toronto's CN tower by staircase and doesn't even draw a breath when he gets there.