Seven years after Sara Polley’s directorial debut, Away From Her, and only two in the wake of her follow-up, 2011’s Take This Waltz, the actress-filmmaker’s latest offering feels like something of a capstone at this juncture of her career. Limited as her body of work may be, Stories We Tell explains, or rather clarifies, her efforts as a narrator; it’s the film that elucidates her pursuits as an artist and even allows us to view them anew through a fresh lens. If her forays behind the camera raised any questions about the thematic drives and interests of her cinema, then Stories We Tell, both gracefully and bravely introspective at the…