It appears that Canada has banned carry-on bags on any flight into the US. This step was taken after the incident on December 26 involving a man and explosives on a Detroit bound flight. I couldn't find out how long this rule is going to be in place...or if it's for each and every flight. You may want to call ahead if you are flying out of Canada. (Remember...that you might be allowed to bring a carryon into Canada, but your return flight into the US might be a different story.)

While carry-on bags are not allowed, they are allowing these items to be brought on:
medical devices
small purses
cameras
laptop computers
canes
walkers
diaper bags
musical instuments
bags containing 'life-sustaining' items