Lots of ways to do this, including many that I'm sure I don't know about.

One place to start would be to research local search volume for "Sushi", "Sushi restaurant(s)", and related phrases -- both in Canada and within comparable regions outside of Canada (especially the USA). You'd want to pay attention to multiple search engines, especially Google and Bing.

That's only a subset of the data you'll need, but it's an important component in the overall picture.