New Brunswick shares a border with Québec and Nova Scotia and an international border with the State of Maine. New Brunswick has an ocean border on the Atlantic Ocean and the Bay of Fundy.
Crossing the international border requires a passport and an inspection, which can include a vehicle inspection. Depending on the situation, a visa may also be required. Different regulations apply to pedestrians and motor vehicles than to boats and aircraft. Depending on the mode of transportation, different ports of entry may be required.
Travelers who frequently travel to and from Canada may want to investigate the CANPASS and the NEXUS cards which provide an expedited border clearance process for low-risk, pre-approved travellers into the United States (or into Canada).