v10superduty is right on. The Canadians do NOT require a passport to enter their country. All a U.S. citizen needs to return to their own country is "PROOF" of U.S. citizenship. Your expired passport will show that you are (or once was) a U.S. citizen. The only way to loose U.S. citizenship is to renounce it. As long as you have not renounced your U.S. citizenship you will be allowed to re-enter your own country. As long at the photo on your passport has similiarities to your current physical state, you will have few or no issues at the U.S. border. If I were in your same situtation I would have with me a current photo document issued by the goverment (driver's license) and a ledgible copy of your birth certificate. These additional documents plus your expired passport will grant you re-entry into the United States by any and all U.S. Customs and Border Protection (CBP) Officers. Good luck. Safe travels.
Lakeside