Citizens of the U.S.A. require a Passport for entry into Mexico and as of March 1, 2010 Canadians will also require a Passport to enter Mexico.
You can find all current Passport Requirements at the U.S. International Travel site:
You are allowed to enter free of duty any purchases with a combined value of up to USD $400.00 For Canada the amount is CD $500.00 IF travelers have been outside of Canada at least seven days. This allowance may be claimed every 30 days. With a verbal declaration a returning Canadian resident can claim duty-free entry for articles (excluding tobacco products or alcoholic beverages) that do not exceed a total value of CD $20.00 upon return from each trip of more than 24 hours.
For the U.S. this limit does not include items listed on the Generalized System of Preferences List (G.S.P.), which are allowed in duty free.
Contact the U.S. Treasury Department for a detailed updated list (Dept. of the Treasury, U.S. Customs Service, Washington , D.C. 20229 ).
For more information: Mexican Customs Regulations
This information is guideline only and following up on government websites for the most current information is highly recommended.