You can sign up for Google Voice, that's what I use when calling the US from Canada. It just uses Data but not too much.
You'll need an App to use it though while you're in Canada - try GooVe IP or Talkatone.
Also you can use skype2go which does charge 2.99$ a month but doesn't use any data. Paired with an unlimited minutes or nights and weekends plan it's an Excellent value. I use it to call my family in the USA.