I've only flown one booking in J with both BA and AC and have to say that Air Canada (particularly LHR-YYZ both ways) left a much better impression on me. The seat was spotless and really comfortable with a great IFE screen. The food was also excellent...I couldn't fault it, and a nice expresso served at the end.

With my Club World flights the crew were quite attentive during the service, but then I didn't see much of them. That's not to say that if I had called they wouldn't have helped/provided, but the crew on the AC flights were much more proactive offering snacks and drinks throughout the flights.

There was a particularly nice female purser with a Scottish accent on the YYZ-LHR flight who was really top notch, such a joy to meet and have a chat with her.

I actually preferred the lounge at Toronto to BA's Flounge, much fresher food and lots of nice places to sit. AC's Heathrow lounge was almost empty!

Regarding AC meal presentation, here are pics from AC869 LHR-YYZ.