ENGLISH-SPEAKING Canadians offer a piquant regional variation within the North American cultural community. That is not to say that all Canadians act or sound the same, or that Joni Mitchell, Jane Siberry and Leonard Cohen, all of whom have released records recently, speak with a unified voice.

All three of these artists are folk-rock singer-songwriters, the kind of person who in the 1960's was called a rock poet - before it was decided that the term sounded too pretentious. Rock poets they remain. Miss Mitchell and Mr. Cohen date back far enough to have had the tag applied specifically to them, and they represent a cool, crisp, wordy, outsider sensibility that somehow reminds one of Canada, even if they may have traveled the world and created these particular records far from home (England and Los Angeles for Miss Mitchell; Paris and Los Angeles, as well as Montreal, for Mr. Cohen; Toronto all the way for the younger Miss Siberry).

Of the three, Miss Mitchell is the most famous and has created deeply haunting work in the past - the past being as recent as a decade ago. But hers is the biggest disappointment of the three. Miss Siberry is a sometimes arch art-rocker whose new disk, by purging some of her affectations, has caused her admirers to fear that she's selling out and some of the rest of us to welcome her greater directness and accessibility.

Mr. Cohen, who has lurked like a beatnik troublemaker on the outskirts of rock for years, has made one of the finest records of his career, certainly the best of these three and a strong candidate for one of the best records of the year.

Miss Mitchell emerged as the cool, blue poetess of Laurel Canyon in Los Angeles 20 years ago. Her first disks defined a limpid, folk-rock soulfulness, with evocative lyrics, neatly crafted songs and a distinctive folkish voice.

But by the early 1970's she had developed a busy, nervously intense style that owed something to Crosby, Stills and Nash and something to a growing interest in jazz. At the outset of this experimentation, she was inspired into some of her finest work: "Court and Spark" of 1974 remains her biggest commercial success, and "Hejira" of 1976 was perhaps her greatest achievement. But other such efforts degenerated into artsy self-indulgence, and too often her collaborations with jazz and jazz-fusion musicians merely diluted her song structures into quasi-improvisatory melisma.

Six years ago, she married the little-known jazz bassist Larry Klein. Her new album, "Chalk Mark in a Rain Storm" (Geffen GHS 24172, all three formats), was produced by Miss Mitchell and Mr. Klein, who co-wrote three of the songs (two others were arranged from other sources by Miss Mitchell, leaving five solely by her). The album, heavily promoted as a comeback, also features a raft of guest stars, including Peter Gabriel, Don Henley, Wendy and Lisa, Billy Idol, Tom Petty, Thomas Dolby and Wayne Shorter.vBut the result sounds oddly, almost aimlessly diffuse. What distinguished Miss Mitchell's best work was a thrilling precision of imagery and musical underscoring, arresting ideas and verbal pictures deepened by the forceful, wistful inflections of her voice and a musical idiom that blended folk, jazz and rock in a compelling way. Here, despite flashes of her old form, the poetry seems flat and generalized (the best is found in a song called "Snakes and Ladders," which makes a neat metaphorical connection between love and the title phrase) and the music watery and faceless in the worst jazz-fusion manner. The best overall moments come when Miss Mitchell sounds most on her own, as in a busily fractured song called "The Reoccuring Dream," which is more like Jane Siberry's work than anything else on this album.

Miss Siberry represents a generation after Miss Mitchell, but there are clear parallels between her use of popular means for overtly artistic ends and what Miss Mitchell and her peers tried to do years before. Miss Siberry also recalls Kate Bush of England and the Roches and Laurie Anderson of the United States.

But with her manic shifts of viewpoint, her miniature dramatic scenes and her quavery, little-girl soprano, Miss Siberry is very much her own person. To this taste, however, her past records and stage shows have pushed too far toward arch little skits and precious self-indulgence, despite moments of simpler, more telling intensity.

Her new album, "The Walking" (Reprise 25678, all three formats), might seem more cynically pop-oriented, but it's just more focused and effective. All her virtues of unusual song structure and arrangement and bizarre persona are still very much in evidence; this material will fit into her older work with no awkward seams showing. And yet the accessibility of songs like "Red High Heels' ' and the eerie work "The Lobby" suggest a welcome maturation.

Maturation is one thing Leonard Cohen hardly needs: he's sounded like a groaning old crank for decades, even if his unquenchable Romanticism still can appeal to an adolescent soul. In any event, his first album in four years, "I'm Your Man" (Columbia 44191, all three formats), is a masterpiece, pure and by no means simple.

Mr. Cohen is a true descendant of the talking poet kind of rock singer; I believe he was No. 348 in the certified sequence of 4,012 critically acclaimed ' 'new Bob Dylans." His songs live for their words, which offer line after line of involving, fascinating images and ideas. His world is that of a defiant middle-aged romantic; this disk is Mr. Cohen's equivalent of Frank Sinatra's 1965 album, "September of My Years." But there is a dark wit here, too, and an ability to see the world with a tougher, crueler, blunter vision than the rest of us can manage.

Mr. Cohen's poetry is by no means all he has to offer. His music sounds classically simple yet fresh, enlivened by apt and original arrangements, mostly by himself and featuring contemporary electronic timbres that don't even hint at a pandering to contemporary tastes.

Even more crucial to his impact is his voice, a gravelly bass-baritone, and his utterly personal phrasing -scansion that transforms innocent-looking lines on the page into rich double and triple meanings. Jennifer Warnes, who appears here as a backup singer on several songs and does just fine in that capacity, came out with a whole album of Cohen material in 1986, "Famous Blue Raincoat" (it contains two of the songs on this new Cohen album). And it sounds hopelessly bland; Mr. Cohen's songs may not need Mr. Cohen to perform them, but they blossom when he does so. If anyone should attempt another all-Cohen collection, it should be someone similarly world-weary, like Marianne Faithfull or the younger artist closest to Mr. Cohen in spirit and sound, Tom Waits.

The most immediately striking song here is called "Take This Waltz," the lyrics adapted from Federico Garcia Lorca and transformed by Mr. Cohen into dark, intense sexuality. But the decadent gloom of "First We Take Manhattan," the obssesiveness of "Ain't No Cure for Love," the moving self-affirmation of "Tower of Song" and, above all, the Brechtian cynicism of "Everybody Knows" all add up to a great record.

Buy it: it may bring Mr. Cohen some richly deserved commercial success. But even if this album doesn't top the charts - it's probably too adult and subtle for that, although the same thing was said about Suzanne Vega - it will remain as an important testimony to the power of the folk-rock idiom to nuture important poetic statements.