Yes to the first question, although whether they will go to the hassle of going after you in a foreign jurisdiction is open to question.
Maybe to the second question, the US and Canada do use the same credit bureau companies.
Possibly but probably no to the last question, depends on whether they put in a complaint and the
flight to avoid payment is a criminal offence. If it's just civil, i.e. they file against you for the money, then that doesn't stop you from travelling to the US. If they file suit in the jurisdiction where you lived and win, there may be criminal penalties if you don't comply with whatever the court says you're supposed to do. Basically anything that rises to the level of a criminal offence might get you denied entry to the US.
The point is that as far as the court and the bank know, that jurisdiction was your primary residence so they will file suit there. The collection agency will try and track you down though. But collecting from someone in a foreign country is hard.
Steve.