Effective June 1, 2009: Canadian citizens will be required to present one of the following U.S. WHTI-compliant (Western Hemisphere Travel Initiative) documents when travelling to, through or from the United States by land (original documentation, no photocopies):

• A passport; or
• A NEXUS card; or
• A Free and Secure Trade (FAST) card; or
• An enhanced driver's license (EDL) or enhanced identification card (EIC) from a province where a U.S.-approved EDL/EIC program is in place
• For those 15 years and under a birth certificate
  
  The Federal Government is seeking approval for the CIS (Certificate of Indian Status) as a WHTI-complaint document.  If accepted, this document will be added to the above list.

The list of ID requirements above is only a summary and details should be verified by the relevant federal agency. 

If you are a permanent resident of the U.S., you should bring your Permanent Resident Card (i.e. green card) with you.

For more information visit:
U.S. Department Of State (*see under VISAS AND TRAVEL DOCUMENTS heading);
or Canada Border Services Agency 
or call U.S. Immigration at (313) 963-4408 / (313) 568-6020, or Citizenship & Immigration Canada Call Centre at 1-888-242-2100.

Related Link:  www.crossingmadeeasy.com