IT`S CLEAR THAT the mystery story is alive and well and living in Canada. Less than a decade after the appearance of a similar collection (Maddened by Mystery, edited by Michael Richardson, Lester & Orpen Dennys, 1982), Alberto Manguel has managed to unearth a respectable group of mostly new tales for Canadian Mystery Stories (Oxford University Press, 296 pages, $17.95 paper). In his thoughtful introduction, Manguel points out that the Crime Writers Association of Canada was founded in 1984 "acknowledging the stupendous rise of a new national genre" What helped to make "this flourishing" possible, he suggests, was such earlier fiction as Kamouraska, the Deptford trilogy, and Surfacing, which "dramatized the Canadian landscape" as "a place of mystery." Of the 20 stories included here, 11 are set in Canada. Geographically, they range from British Columbia to the Maritimes; artistically, they range from Alice Munro`s characteristically subtle "Fits," about a small-town character`s reaction to her gruesome discovery of a murder-suicide next door, to Edward O. Phillips`s "Solstice," in which an ingenious plot overcomes the handicap of stilted prose. A few - notably Munro`s story; Eric Wright`s "Twins," about a mystery writer who plots the murder of his wife; Laurence Gough`s "Big Time," about an armed robbery caper that runs afoul of female ambition; and Tim Wynne-Jones`s "The Imposture," about irregular activities in a graveyard - are good enough to be included in a collection of best stories from any genre. All in all, Canadian Mystery Stories is a heartening sign of health and strength at an uncertain time in our literary history.