(French) feminine form of Michel, the French form of Michael. This name is now also used extensively in the English-speaking world. It was popular in the 1970s and 80s, possibly influenced in part by a Beatles song with this name as its title (1966).
Scottish: regional name from a district north of Aberdeen. There was also a barony of Buchquane in Strathore, Fife, a settlement called Buchan in Kirkcudbrightshire, and several other places in Scotland so named, but these are less likely to be the source of the surname.