Hi I asked on the aircanada website thread, but no one replied and this issue is not just on the AC website but all websites lately

On some routes, especially if it includes a segment to the USA AND has a Dash-8 flight there does not seem to be a way to book the flight in business.

Use a sample quite date with lots of availability such as January 16 - January 23
Use a route such as Victoria, Naniamo, Kelowna etc that has dash 8 service. You will find you cannot buy a business class ticket to say Las Vegas for example. Even a trip to YYJ-YYC there are many cases that you can't buy a business class ticket. The flights are empty and the loads are low so its not an availability issue. I have purchased lots of J tickets in the past but now all post as UNAVAILABLE

As well to make things more confusing, EXPEDIA and TRAVELOCITY etc will let you book, but at the very end, with very little on screen notation, they change your flight from business to economy. Its very confusing and frustrating and would love to know if there is any workaround.