The fuselage of a Boeing 777 has a diameter of about 3.7 meters, or about 12 feet. So you're looking for something that's less than 4 meters high, and less than 4 meters wide. If it is more or less intact the wreck might be pretty long, so on a reasonably flat ocean floor you might pick it out at 10 meters resolution, but in less ideal conditions you might need closer to 2m resolution to make it stand out against the background. There are the wings, which are very big, but also very thin, so their usefulness really depends on how they are angled.

What we have are pretty good 400x400m maps, and increasingly more 100x100m maps.