To clarify, it's not Canada that will be requiring the passport, but the U.S. will require them to get back into the States. This will take effect for travelers to/from Canada at the end of 2006, as mentioned.
If your birth name has changed (for example, by marriage) you should bring also a certified copy of your marriage certificate, as well as the certified copy of the birth certificate and your photo ID. Hospital birth certificates and photocopies of birth certificates are NOT acceptable. The certificates must be of government issue (county or state ok) and must include some kind of official signature and/or seal. Needless to say, if you have a passport, it's much easier to bring that along instead - one form of ID instead of 2 or 3!