Canadian used to fly 737s into YTH, routing them through YFO or YQD (Flin Flon or The Pas). In the late 1990s, they cancelled the 737 service (nothing to do with AC), replacing it with some nonstop F28s to YTH. Calm Air took over flights to YFO and YQD. Canadian Regional dropped the F28 service to YTH a few years later, and Calm Air added some codeshare flights on their SF3s to replace it. The jets weren't being filled, and could be better used on other routes.
I'm not surprised that YTH can't support a 737 ... it's only a city of about 15,000 people.
[This message has been edited by StuMcIlwain (edited 10-05-2002).]