What is the real-world location of the house used as Dr. Louise Banks's home in the movie?
The script and film are intentionally vague on the subject. Louise appears to be an American national (and her students have American accents) which would imply that she lives in America somewhere but there aren't any obvious markers. Her house is simply described as "Lake House", the university is simply "University Classroom".
Note that her university's name isn't shown and the hospital where she has her daughter is described as "Mercy Hill Hospital", a fictional place. The numberplates in the university car park don't conform to any US or Canadian plate style.
No help here. Chiang's short story doesn't contain any location markers, nor any mention of Louise's house.
The interior shots for the film were shot in and around Saint-Fabien in Quebec. This interview (and the answer below) confirm that the house was an actual location, rather than a set. The exterior driveway shot was filmed in L'Île-Cadieux, Québec, as were the interior shots of her house looking out over the Lake of Two Mountains
For the record, the exterior (university) shots were filmed at the Université de Montréal, Quebec.
Here is the Streetview of the house. It's in L'Île-Cadieux, Québec.