yes any border patrol / border guards can do background checks and ask any questions including whether or not someone has committed a crime and that crime got dismissed because of mental illness. they have to ask in order to determine whether the person crossing is doing so to avoid going to prison or a mental hospital. they have to ask in order to determine whether the person crossing is a danger to their self or others or the country that they are entering. I have crossed from NY to Canada many times as I have a relative there.

one thing you need to remember is that here in America the border requirements keep changing so coming back to the US from Canada is much harder and stricter. they don't prevent an American from coming back to America but if once on the American side if anything comes up wonky so to speak when American border people do their background and such, a person could be detained until certain documents have been procured.

my suggestion is that before you go crossing the border again, make sure you have all your documentations that ...Both...… countries may require not just what one side or the other requires.