Do you need a passport to travel to Canada?
yes, you do nowadays. I went on a cruise to Alaska in the fall which departed from Vancouver, BC, Canada. I had to bring my passport to get into Canada and I had to bring my passport to get back into the US.
In most cases, US citizens do not require a passport for short visits (less than 180 days) to Canada. However, a citizen must provide documents like a photo ID or a current driver's license. Check out http://travel.state.gov/travel/cis_pa_tw/cis/cis_1082.html for more information.