Canada

You can read about 338Canada's Methodology in their About Page.

In answer to your questions, some polls break down their results by region and very rarely (but sometimes) there is riding specific data. Poll Aggregators have to careful about these as they sometimes involve small sample sizes. For example, I think Philippe was talking about one in the last couple years that broke down their results by province, but PEI only had 42 responses (that's like 3884 Ontarians per capita, which is a good sample size) which is too small a sample to consider so he just aggregated the Atlantic provinces. Riding specific polls are also rarely useful due to small sample size, infrequent polling, and questions about their methodology.

The secret sauce of these poll aggregators is how they rate polling firms/methods and how they weigh ridings for past performance, shifting demographics, and current candidates. If you're curious for more, I like listening to Philippe and Éric Grenier talk about polling on The Numbers podcast.