One of my favorite local authors, Ellen Percival wrote an interesting article on flying with kids. http://www2.canada.com/topics/travel/story.html?id=804659
One of her tips included:
” If you are one parent travelling alone with your child, you will need the long version of the birth certificate as well as a notarized letter of travel consent signed by the absent parent.”
On my last trip back through customs (without my husband) I had a rather tough officer who gave me the evil eye when I showed him a letter my husband had signed authorizing me to travel alone with the kids but it was not notarized. We had crossed the border together with the kids but my sister and I flew home a week later with the twins.
They let me through, but it made me think twice about getting a proper note the next time!