Yes, to work in the US, a Canadian citizen will need a work visa, just like any other foreign national. Those are the H-1B, O-1 (if extraordinary in one's field) or specific for Canadian and Mexicans, the "TN" Treaty Nafta work visa valid in 3 year increments.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Canadian citizens enjoy many benefits int he US but he or she will need a work permit nonetheless. Speak to an attorney to see what options are available based on the profession of the applicant and employment opportunities n the US.