Green’s Dictionary of Slang

(US) Canadian.

1862		Congressional Globe 29 Apr. 1867/3: They went from St. Louis to Canada to buy the little Canuck ponies at $130 apiece.
1904		Sun. Times (Perth) 21 Feb. 4/5: The Canuck Government [...] will probably tell the brassy little Jap to get his head read.
1962		Kerouac letter 9 Oct. in Charters II (1999) 350: Himself speaks only a touch of Iroquois. And of course the same Canuck French as all over Canuck Canada.
1986		S. King It (1987) 869: Claude Heroux was, according to Thoroughgood, [...] One bad Canuck son of a whore.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 37: One Canuck doctor — François Bondurant.