IN HIS THOUGHTFUL and eclectic Some Day Soon: Essays on Canadian Songwriters (Quarry, 176 pages, $16.95 paper), Douglas Fetherling considers the careers of five Canadian songwriters: Gordon Lightfoot, Leonard Cohen, Joni Mitchell, Robbie Robertson, and Neil Young. The book addresses not only the performers` musical evolution, but also the degree to which they retained links with Canada while achieving varying degrees of fame in the United States and elsewhere. Fetherling`s combination of cultural and musical commentary makes for genuinely interesting reading. Throughout, the tone is informative and entertaining. Fetherling`s opinions often challenge the reader to think about music from a host of innovative viewpoints. Some of these are surprisingly insightful: "...country music depends for its success on an ability to resist change at the proper speed." Others are wryly amusing: "Collaboration with Willie Nelson is always a sign of a musical career in panicky transition." And Fetherling is never reluctant to consider his subjects from an unexpected angle, as in his description of Joni Mitchell as a "kind of rock `n` roll de Tocqueville." Some Day Soon`s wide-ranging essays will appeal to anyone with an interest in what was a fertile and dynamic period in North American popular music. The discography is also a welcome inclusion.