I have flown this route with BA, AC Rouge and AC. Air Canada wins hands down. BA told us that despite booking 10 months ahead we didn't have seats. Rouge is equivalent to the cheap airlines therefore one has to pay for everything bar the basics. AC treats one courteously, takes care of luggage from start to finish and doesn't mess about. You also get a choice of meals and alcohol; on a transatlantic flight, methinks this is important.