In most cases, citizens of Canada do not have to have a visa to enter the U.S. as long as their purpose in the U.S. is for studying or visiting. If you enter the U.S. by air, though, a passport will be required. Those Canadians that enter the U.S. by sea or land must have a Western Hemisphere Travel Initiative-compliant travel document.
There are some instances in which a Canadian will need a visa. Some examples include fiance or fiancees, intending immigrants and investors must have a visa just as other nationalities. Temporary workers and journalists must have the correct supporting documentation, and that paperwork must be given to a U.S. Customs and Border Protection Officer at the Port of Entry. It's best to look at the CBP website before you travel to make sure you know — and are compliant — with all entry requirements.
For Canadians who have been removed or deported from the U.S., or those having a criminal record, including DUIs,- other requirements must be satisfied before they can enter the U.S.
Canadians who are visiting the U.S. can stay for up to six months, but they can also extend their stay by making a request to the U.S. Citizenship and Immigration service. However, if you intend to work, study or live in the U.S., you must disclose this to the Consular or the CBP officer before entering the U.S. If that is not done, then you may end up permanently banned from entering the U.S. again.
An experienced lawyer can help you learn more about what is needed to enter the U.S. from Canada.
Source: U.S. Embassy and Consulates in Canada, "Information for Canadians," accessed Oct. 14, 2016