Ask nicely... all the North American flights are fully booked these days -- last week, I was flying back to YVR from HKG on CX 838... J was less than half booked, but I got an op up to F (yes...) Y was very overbooked on all these SFO/LAX/YVR flights due to the promotions released earlier in June. If you ask nicely, you will never know...

But be there for boarding -- it was chaotic at the gates, although CX was good in keeping everything in order.