TORONTO – The filmmaking partnership of Scott McGehee and David Siegel has forged what can only be described as an unexpected path. After their 2001 breakout indie thriller “The Deep End” the duo found creative success in family dramas such as “Bee Season” and “What Maisie Knew.” Now, after an eight-year break following “Maise,” they return with “Montana Story,” a strangely thin melodrama held together by Haley Lu Richardson’s captivating performance.