I have to tell you that I've experienced an unwillingness to do this, whether on separate tickets or one ticket. I normally fly YVR to GVA and I prefer to go AC from YVR to LHR and then switch to BA. Up until about 5 years ago, it was no problem and the luggage was switched automatically. Then it became that I had to have one ticket with the two airlines (something that made the costs prohibitive). Then it became that they wouldn't do it at all. So, now I have to through FRA if I have luggage. If anyone knows of anything different, please let me know. I'd rather do the YVR LHR thing because of upgrades being more available.