In the film, the Toronto Sun is published in broadsheet format. In real life, the Toronto Sun is published in tabloid format. The Toronto Star, its competitor, is a broadsheet.
In the film, none of the cars have a front plate. Ontario law requires all vehicles to have both front and rear license plates.
The telephone number on the taxi that drops off the Bernardos after their honeymoon has a 613 area code. At the time, the area code for St. Catharines/Niagara was 905; 613 is the area code for Ottawa and Eastern Ontario.
The film is set in the late 1980s and early 1990s, yet Paul's recording room includes a poster from Incubus' 1999 album "Make Yourself".
When Karla and Paul drive off after abducting a teen, about 56 minutes in, a crew member in sunglasses is clearly visible on screen.
When the police and ambulances start to arrive at Karla's house after the drugging and raping of Tammy Homolka there's a quick glimpse of the speed limit sign which is measured in mph. In Canada the speed is measured in kmh not mph.
In the film, the New York-Ontario border is in the woods. In real life, the New York-Ontario border is made up of the Niagara River, the St. Lawrence River, and Lake Ontario. The New York-Quebec border is in the woods.