We want to find out our Total addressable market (TAM): How big is the market we are currently in? How quickly is it growing? 2. Served addressable market (SAM) We are trying to build a product for sushi style restaurants in Canada.
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.