Hi
YOu should say whether you are a PR or Canadian citizen.
I know that makes a difference when it comes to the spouse but not sure about the mother. So if you let us know about whether you are a PR or citizen, the others might be able to answer you better.
It really doesn't matter, if the mother is not residence in Canada for 2 years in every 5, she loses her PR status. It should be interesting if the US will admit the mother for 3 years.
PMM