What coverage do I get if I'm a British citizen living in Canada traveling to the USA on holiday?
You have many options as a non-U.S. citizen traveling to the U.S. for a short period of time. It doesn't matter much that your citizenship is in one country and your home is in another. You can consider any of the policies here.
In the application of any policy if it asks for home country, you would select "Canada" and if it asks for citizenship country you would select "United Kingdom".
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else