It depends.

US consulates in Canada do issue background checks, if you look into the old posting here around first two quarters of 2003. The only thing we don't know is: what are the criteria for a VO to issue background check ?

My guesses are: 1) your work or expertise is somewhat "sensitive". Like biological or chemical process realted to virus, explosives, or anything smilar or contagious. 2) your job function is too technical to understand, and may lead to connections to the first category. A real story, a friend's friend got backgorund check in Vancouver in summer while applying for H1B visa. Probably because he's working for a high-tech company, and the VO couldn't understand what he does. It's fortunate the check came back in 3 or 4 weeks, and he was issued a single-entry H1B visa to let him go back to work.

My suggestions:1) To eliminate confusions regarding your job function, use plain English and short sentences to explain it in your proof of employment letter. 2) Ask someone not in your field to proof read it to see if people can understand your job function, and not build connections to any categories mentioned above.