Advice needed, replacement for Canon 75-300mm lens for aerial photography

[RKW3]

I have the Sigma 80-400 with OS, and I think it works fine (OS=IS). Not the fastest focus, or the sharpest results, but it works well enough for me. The OS works really well also IMO. It's pretty heavy though, so I'd recommend trying it out with a monopod.

The Canon version is more expensive but it's probably a bit better at focusing and the sharpness, though. If you have the money you should probably look at the Canons.