Factual error: The customs warehouse guards are carrying guns. Canadian custom guards do not carry guns at any time.
Factual error: When Nick navigates through the sewer system, he checks his position using GPS. The position on his display corresponds to the middle of the North Atlantic instead of the Montreal area.
Factual error: When DeNiro scouts out the building by going inside, Ed Norton guides him via a handheld two way radio. Having been a Marine for 5 years and working with various high power communications gear, I have never seen or heard of a handheld two way radio that can talk to another radio that is underground and quite a distance away. Both of the radios were portable meaning they had small batteries powering them, not a powerful power supply. Handheld radios work on the UHF spectrum, which is line-of-sight. It is impossible for a UHF signal to reach a receiver by going through numerous walls and metal piping. Ever lose your signal on your cell phone when inside a building or tunnel? Same concept.
Factual error: The computer hacker says: "I was cruising around Ironclad's server at the root cobol level. when someone counter-cracked me, hacked into my machines, my data. For three minutes, I was fully exposed." The term "root cobol level" is completely made up, and has no meaning to a computing professional.
Answer: He didn't know for a fact that it would happen, but he was experienced enough in these kind of high-stakes operations to plan for literally every contingency, including a double-cross.