Available evidence suggests the codeshare agreement was only on specific routes and not on the YYZ-BRU route. A quick check of the AC timetable also failed to show a codeshare on that route. Here's the most recent & applicable threads on the topic I could find:

http://www.flyertalk.com/forum/air-c...z-bru-jet.html

http://www.flyertalk.com/forum/air-c...tership-2.html