Would a passenger on the US no fly list be allowed to board domestic Canadian flight?
 

A lot of domestic Canadian flights pass through US territory. For example, flights between Toronto and Vancouver spend around half of the time in US airspace. I would therefore expect Canadian airlines to pass APIS data to the US for purely domestic flights as well.

Now let's say a passenger is on the US no-fly list, but is not on the Canadian no-fly list. Will they be allowed to fly on a flight from Toronto to Vancouver? If so, does this mean that in theory there are some Canadians who are forced to drive around the country because they're blocked from domestic flights?

Flights originating and ending in Canada are exempt from US secure flight requirements

Here is a link to Air Canada info on the secure flight requirements. Point to point in Canada the answer is no even if the flight goes through U.S. airspace.

https://www.aircanada.com/ca/en/aco/...t-program.html

However, this was not always the case however. Air Canada has previously used the U.S. no-fly list to prevent people on it from flying within Canada.

https://www.cbc.ca/news/business/no-...nada-1.3500508