The helicopter that brings the Russian president to the White House has U.S. markings on the side, and a Canadian registration number on the belly. U.S. registrations begin with N, Canadian ones begin with C.
During the opening suicide attempt, Roy-Boy has a strip of duct tape over his mouth and another around his wrists. After climbing over the guardrail at Niagara Falls, the duct tape is gone from both his mouth and wrists.
Just as Honey finishes disabling the Hacker Hellstorm, the camera cuts briefly to a clock that stops at "0:08" after a computer falls over and explodes. The camera cuts to the War room's countdown display, which shows the countdown stopped at "T-0:00.8", 0.72 seconds later than the Hellstorm's clock.
The motorcade at the beginning, which is supposed to be in Niagara Falls, passes Dofasco Steel, on Ottawa Street in Hamilton, Ontario. The factory shot from across the water is Stelco Steel, Dofasco's neighbor.
Boomer, Roy Boy, and Kabral are shown having to camp out for a night traveling from Niagara Falls to Toronto, and drive along rural roads to get there. The two cities are actually connected by freeways traveling through densely-populated areas, and can be driven in a couple hours.
In the campfire scene, Boomer, Roy Boy and Kabral are discussing movies and the recurring plot element about the fact that 'the black guy dies' and they mention several examples like Jurassic Park, Unforgiven, The Dirty Dozen, Witness and Alien. The problem with those examples (although accurate in this sense) is the fact Kabral says that the black guy always dies first, and in those movies they're not the first ones to die. However, he got it right with The Shining and Forrest Gump.