If many arthouse films nowadays seem destined to divide audiences into generational camps, the absorbing Canadian drama Away from Her has the welcome effect of bridging the age divide in several senses at once. Credit for that belongs largely to two extraordinary actresses working on opposite sides of the camera.

Born in 1979, Sarah Polley started acting at the tender age of 5 and grew up to convey an evanescent blend of beauty, reserve and laser-like intelligence in films such as Atom Egoyan’s The Sweet Hereafter. Away from Her, an adaptation of the Alice Munro story “The Bear Came Over the Mountain,” is her first feature as writer and director. At a time when many a 20something actor-turning-auteur would be concerned to project youthful currency and hipness, Polley has turned in exactly the opposite direction: Her directorial debut is about a retired couple facing the ordeal of Alzheimer’s.

Born in 1941, Julie Christie was the screen goddess of my youth, an icon of Swinging London in films like Billy Liar and Darling, the radiant star of hits ranging from Doctor Zhivago and The Go-Between to McCabe and Mrs. Miller and Shampoo. Now at retirement age, Christie has elected to do what many stars her age probably wouldn’t even consider: play an Alzheimer’s patient older and more infirm than herself.

The decisions that led Polley and Christie to Away from Her reflect a kindred contrarianism. Both actresses have held mainstream moviemaking in suspicion, have seemed deeply ambivalent about being known for their beauty, and have effectively spurned the compromised commitments of Hollywood stardom. Both are politically engaged and outspoken. It is hardly surprising that any film combining their talents would display countless surface fascinations as well as a bone-deep integrity.

Away from Her opens with a quietly persuasive portrait of connubial contentment. Fiona (Christie) and Grant (Gordon Pinsent) have been married 44 years and now enjoy a seemingly idyllic life in a beautiful home that faces a snow-covered lake. The trouble that will undo their life together appears at first as minor slip-ups: Fiona forgets the word for “wine” and stores a frying pan in her refrigerator’s freezer.

With its gorgeously glacial winter landscapes and a central couple who could easily be played by Erland Josephson and Liv Ullmann, the early sections of Away from Her inevitably recall the fictional worlds of Ingmar Bergman. When Fiona goes out cross-country skiing and loses her way, the mix of horror, love and great relief that crosses Grant’s face when he finds her conveys a sense of life’s existential abysses that is indeed Bergmanesque.

Yet a Bergman drama would typically lead us into ever-deeper levels of trauma and torment, and that’s not what happens here. Polley’s film, it turns out, is less about the horrors of Alzheimer’s than about the practical ways that people experience and deal with this difficult passage. As it happens, Fiona retains enough sporadic lucidity to understand what is happening to her, and it is she who insists that she move to a retirement home.

With a sobering matter-of-factness that undercuts her material’s innate melodramatic potential, Polley shows the couple discussing the challenges of Alzheimer’s, even referencing books on the subject, and she follows Grant on an introductory tour of the retirement home. He evidently finds the place distastefully clinical. Yet the biggest challenge it presents him is one he could not have anticipated.

When Fiona checks into the retirement home, Grant is told that she’s not to have any visitors for the first month, in order to allow her to settle into her new environment. (Reportedly, this policy, once practiced by some Canadian retirement facilities, is no longer common.) Grant is left at loose ends, of course, grasping at the strange emptiness that his life has become. When he finally visits his wife, he’s chagrined to find that she barely notices him and instead lavishes attention on a fellow Alzheimer’s patient named Aubrey (Michael Murphy)her new beau, it seems.

Apparently, Aubrey knew Fiona as a teenager and had an unrequited crush on her. Now age has given them the chance to form a bond that youth denied them. To Grant, this attachment is a prod not so much to jealousy as to bafflement and the sense that his wife’s slow deterioration produces an ever-deepening estrangement between them. There are also hints of a guilt that haunts him as a result of infidelity on his part, long ago when he was a popular literature instructor and sexual mores were in flux.

These flashes from the past are part of the subtle, carefully rendered emotional textures of Away from Her, a complexity that also characterizes Polley’s most ingenious narrative ploy: Grant goes to visit Aubrey’s wife Marian (an excellent Olympia Dukakis), and rather than being presented as a single scene in the story’s chronology, the encounter is broken up into several small scenes which are interspersed throughout the tale. The effect is to keep us wondering about Grant, his motives, and the place that Aubrey and Marian will eventually occupy in his life.

For it is his life that we are ultimately considering. If in some of the film’s early scenes we seem to be witnessing events from the couple’s shared viewpoint, from the time Fiona enters the retirement home, we are clearly looking through Grant’s eyes and will continue doing so until the final fade-out. This has interesting implications on many levels of the film, not least that of the performers. I don’t believe I’ve ever seen Canadian star Gordon Pinsent before, but his work as Grant is little short of masterful. It’s a brave, solid, expertly controlled performance and never more so than when he gazes at Fiona with his understandable blend of tenderness and apprehension.

As the object of that gaze, Christie has natural attributes that make her almost uncannily suited to playing Fiona. Though it’s odd to hear a flat Canadian accent coming from this most British of visages, the exquisite lines of her face have grown only more striking with age, and her now-white hair and pallid skin make her seem almost translucentan angelic presence even as she fades into another dimension.

Is she a great actress? I was so enraptured by Christie way back when that I never stopped to ask this, and so was caught up short recently in seeing David Thomson’s judgment in his Biographical Dictionary of Film: “She is, sadly, obvious in her efforts, lacking either gaiety or insight and, most serious of all, gawky, self-conscious, and lantern-jawed. She grins rather than smiles, and her movements are either nervously darting or ponderous.” Even if one grants that this harsh evaluation might have fit Christie’s work as an ingénue, but not the seasoned accomplishments displayed in films like McCabe and Mrs. Miller and Don’t Look Now, Thomson’s words touch on a quality of Christie’scall it a sketchinessthat courses through her work, and often not to its detriment.

Discussing her star in the current issue of Filmmaker magazine, Sarah Polley puts it this way: “[A]s a person, she’s so ephemeral, really. You fall in love with her instantly, she’s so engaged and engaging and curious and kind of wondrous. But she’s sort of with you one minute completely and then absolutely gone the next. So, in a way, on a one-on-one personal level, you’re always chasing her. You’re always trailing her around like some broken lover. I think everyone has that experience of her, whether they’re an audience member or a friend, and I felt like that’s sort of what this character needed, this sense of, Is she with you now or gone? Is this a charade or is this real?”

That alluring elusiveness not only makes Christie the perfect Fiona, it also clarifies and enriches Grant’s view of herand Polley’s. Though Away from Her has occasional moments that seem strained or rhetorical, it is a hugely impressive work coming from a filmmaker in her 20s. If some viewers may feel that it skirts the most searing agonies of Alzheimer’s, it is finally not a film about the disease but about a love that survives and transcends it, and on that level, it’s remarkably wise and hopeful.

Away from Her opens Friday in select theaters.