Which of the following states shares a border with Canada?

Maine shares a border with Canada, making it the correct choice. It is the northeasternmost state in the United States and has a long boundary with the Canadian province of New Brunswick and a portion of Quebec. Maine's geographic location provides an important link in terms of trade and cultural exchange between the two nations.

The other states listed do not share a border with Canada. Florida is located in the southeastern part of the U.S. and is bordered by the Gulf of Mexico and the Atlantic Ocean, but not by Canada. South Dakota is situated in the north-central part of the U.S. and shares its borders with several states but does not reach Canada. Georgia is located in the southeastern U.S. and is bordered by several states as well, none of which connect to Canada. Thus, Maine stands out as the only state in this list that shares a direct border with Canada.