Nikon 800e or canon mark3?

I'm a wedding and portfolio photographer in india.
Please help me which camera i should buy Nikon 800e or canon mark3

And welcome to Y! A Camcorders:

You are asking about two digital "still-photo" cameras, and this is the "Camcorders" category. I know you also posted this same Question over in "Cameras" (you have a bad habit of posting all your Y! A Questions in 2-4 different Categories at the same time!).

For wedding photography (portraits & stills) either camera model should serve you fine. Just take into consideration your total budget limit and the cost of lenses and other accessories. (Historically, Nikon accessories & Nikkor lenses cost more than Canon brand.)

As far as shooting video, keep in mind that DSLRs have time-limits on how long they can shoot in "Live" mode (due to file size limits and overheating issues). You won't be able to "film" continuously without stopping or the camera overheating & shutting down after 30 minutes.

(I've worked at many India/Hindu wedding ceremonies, and they last a long time!)

Here's a good comparison review between the two models with shooting video footage: http://www.mikekobal.com/blog/?p=4718

If you are already an established wedding & portrait photographer, you probably have several cameras in your collection. If not, keep in mind that most professionals own several cameras, and you should consider owning separate camcorder gear (a real camcorder, not a still-camera with video "features") as well as a good DSLR.

As far as building a good equipment collection for the future, consider looking at something like the Sony NEX series, which has both still-photo and full-camcorder models, and which can share the same lens accessories. (Sony NEX-5/NEX-7, and NEX-VG20/NEX-VG30 all share the same E-mount lenses.)

I listed other model-specific (Canon / Nikon) reviews in my Sources below.

hope this helps,
--Dennis C.

The D800e is a superior camera in my opinion.