Green’s Dictionary of Slang

(US) a large foot or shoe.

[1890		Ottawa Free Trader (IL) 5 Apr. 7/4: Some of ’em are too pointed, some are too broad, and most of ’em make my feet look like canal boats. Damn the shoes, anyhow].
1896		Scranton Trib. (PA) 9 Jan. 2/3: He appeared on the stage wearing ‘canal-boat’ shoes.
1916		Honolulu Star-Bulletin (Oahu, HI) 1 Jan. 8/1: [Charlie Chaplin’s] make-up was as near perfect as could be imagined, including the absurd moustache and the ‘canal boat’ shoes.
1926		Maines & Grant Wise-crack Dict. 6/2: Canalboats – large sized shoes.
1939		‘Flann O’Brien’ At Swim-Two-Birds 121: He is standing as you find him with his blue pants and his big canal-barges on his two feet.
1948		S, Paige Pitchin’ Man 29: If I had big feet the kids woulda called me ‘Gunboats’ or ‘Canalboats’.
1951		in DARE.
1960		(con. 1950) R. Leckie March to Glory (1962) 94: Hey, Moose, when I die I want you to take my boots to keep those canalboats of yours warm.
1960, 1975		Wentworth & Flexner DAS.