ACCORDING TO JAKE AND THE KID by W.O. Mitchell (McClelland & Stewart: $12.95; 280 pp.). Although his work is little known south of the border, W. O. Mitchell ranks among Canada's foremost humorists. This anthology chronicles the misadventures of an adolescent boy growing up on a Saskachtewan farm during the '40s. In all things, he is assisted by Jake, a combination handyman, rural philosopher and substitute father. Although "Jake and the Kid" are often comic, they're never buffoons. The gentle, tongue-in-cheek tone of Mitchell's stories recalls the work of many Midwestern writers, suggesting the North American plains inspire a uniform reaction that transcends national boundaries.