For flying, the Bose QuietComfort Ultra (2nd gen) has the edge: it blocks more engine noise and folds into a smaller case. The Sony WH-1000XM6 sounds better and is the more natural, less pressurised listen, which makes it the better all-rounder if you'll wear them as much on the ground as in the air. Frequent long-haul flyers: Bose. Everyone else: Sony. Both are excellent; you won't regret either.
Noise cancelling at 11,000 metres
Engine drone is low, constant rumble, exactly what noise cancelling is best at, and both cut it dramatically. Reviewers who've compared them side by side find Bose blocks a bit more, with a stronger "vacuum" feeling, and lets you set how much. Sony's cancelling is more subtle and natural, which some people find more comfortable over many hours. On a 14-hour flight to Manila or Delhi, if you're sensitive to that pressure feeling, Sony may be easier to live with; if you want the quietest possible cabin, Bose.
Battery: a draw
Both quote about 30 hours with noise cancelling on, which covers Toronto to Hong Kong and the flight home before you need to charge. Bose's immersive audio mode cuts its figure to about 23 hours, so leave it off on the plane. Either way, charge them the night before: on international flights you can't use a power bank to charge in the air.
Seatback screens
Both come with a 3.5 mm cable, so they plug straight into the seatback screen, and both keep cancelling noise while wired. The Bose also plays audio over USB-C, handy with a laptop or a phone without a headphone jack. A few older planes have two-pin sockets: a small two-prong airline adapter weighs nothing.
Packing and comfort
The XM6 folds now (the XM5 didn't), but it still stores flat in its case. The Bose folds its earcups inward into a smaller bundle, which matters when your personal item is all you've got on a Basic fare. They weigh almost exactly the same, about 250 g. For sleeping sitting up, reviewers find the Bose softer with less clamping pressure, and the Sony more secure with a wider headband. If you sleep against the window, earbuds like AirPods Pro 3 will be more comfortable than either.
Our call
For a traveller who does a few long flights a year, the Bose QuietComfort Ultra (2nd gen): quieter cabin, smaller to pack, wired over USB-C. If you'll use them daily for music and calls and fly less, the Sony WH-1000XM6 for its sound and fit. On a tighter budget, the older Sony WH-1000XM5 has the same quoted 30-hour battery and is often cheaper.