Where fact-fiction hybrid documentaries are concerned, the game of wondering what's really "true" can too easily degenerate into mere indulgence, leaving behind little more than just those quotation marks. Alternatively, more rarely, it can be a blessed riddle. In Stories We Tell, an exemplar of the form, the perceptive Canadian actor-director Sarah Polley gathers her extended family for a collective documentary remembrance of her late mother, Diane, who in retrospect seemed all too comfortable at the center of so much attention. On the other hand, Diane also had at least one whopper of a family secret, which Polley rather politely but ardently wants to get to the bottom of. On this matter, the rest of the family is both a great help and no help at all. Arguably they incriminate themselves, but Polley's plan isn't to corner anyone; her heart is much too huge for that. Deep within the cozy nostalgic enclaves of bohemian Montreal and Toronto, some thorny questions do come up for Diane's most significant suitors: Polley's sweetly reticent father, Michael, himself also an actor and a writer (at Polley's command, he overlays the film with his own beautifully literate narration of family lore), and Harry Gulkin, a gregarious film producer. Generously, young Ms. Polley presses on, recognizing that what's really at stake is her own origin story, and that sharing it is the best way to validate it.