What color grading tool you suggest now?
For Final Cut Pro X I don't know. Maybe Colorista II? Others would know better than me.
I find out that vdo file from Canon DSLR look so soft that look great in small resolution, but when scaling to larger size it looks so soft and lost some detail.Do you think if I sharpening with some color grading tool could be help?
Color grading, or at least color correction, always helps. I apply some color correction/grading to every single clip, even for YouTube, even if it's just to control the black or white levels.
Why are you scaling to a larger size? What resolution to what resolution? I have a method to upscale from 576i to 720p and as the very last step before encoding to mp4 for the net I apply a sharpen fx (in Vegas) with a value of zero, which still gives it just a little sharpening. The only clips I don't do this on are those with lots of noise, because sharpening accentuates noise.
By the way I saw some footage from Panasonic GH2, the vdo file looks great for detail and sharpness.
Yes, GH2 is great in both those respects. Underwater the biggest problem is banding, especially in highlights around sunballs. Can get very ugly for wide shots looking towards the surface.
I didn't see any improvement of vdo file from Canon latest model such like 5D MkIII,6D.
From what I've read and watched, 5D MkIII is a better camera for wide-angle than the GH2. The bigger sensor makes it better in low light and there are better wide ports for it. Check out Berkley White's Cenotes Mexico video. Even topside the 5D MkIII footage benefits from some sharpening, but maybe not necessary if downscaling from 1080p to 720p.
What do you think about the new comer GH3?
From what I've read and watched, better in every way than GH3 except for a little moire/aliasing, which doesn't really affect underwater shooters except for shooting tank mesh! It sounds like the banding and highlight handling is better than GH2. Will wait and see. I know of no glass ports for GH2 housings. Hopefully there will be for GH3. Also people were doubting that the available ports for GH2 were optimized for any of the wide angle lenses. That means distortion. Apparently the Nauticam housing is on the way in January.