Yes, however I was told by an AAgent that AA RTW desk cannot book all AA codeshares even if they exist. It's specific to the operating airline and route, and they don't know until they try booking the segment. However, the agent said if the route is to/from US, they can def book the codeshare.. but outside of that arrangement, YMMV. Thus, because this is a codeshare between UK and Canada, it may not be possible.. but worth asking about. This was a relatively recent rule in the past 12 months, per the AAgent.