Has any governor of Maine ever vetoed a bill that would have legalized same-sex civil unions in that state?
Not sure I understand the question correctly, but I will try to answer. The State of Maine has a governor, a state legislature consisting of a House of Representatives and Senate, and a judicial court system of District, Superior, and Supreme Courts. Maine does not have a Lieutenant Governor or Assistant Governor.
That is an interesting question, because some countries, like Canada, do have a "governor-general." But the United States does not. It has a President and a Vice President who run the federal government, and each of the fifty states has its own governor. To find out the current governor of each state, go to the web page of that state, and it should tell you. But since you selected "Maine" as one of your categories…
Cliff Finch (born April 4, 1927 in Pope, Mississippi; died April 22, 1986 in Batesville, Mississippi) succeeded Bill Waller as the fifty-sixth Governor of Mississippi, serving between January 20, 1976 and January 22, 1980. Following the end of Finch's term as Governor, William Winter (born February 21, 1923 in Grenada, Mississippi) became the fifty-eighth Governor of Mississippi, serving between January 22, 1980 and January 10, 1984.