Now shall I sell my current main lens, Canon EF 17-40mm f/4 L USM lens?

I think it depends greatly on what you shoot.

I just recently bought the 17-40 to add to my arsenal, as I found the 24-105 to be too narrow at times. Besides that, the 17-40 seems a bit sharper, with less distortion, than the 24-105, up to about 35.

But only you can decide how many lenses are too many, and which ones you really need.

Yes, 17-40mm is fantastic for landscapes but not so great as general lens. When I shoot people and forget that I am using 17mm they look funny when they are close to edges of the frame. With small sensor it was more like 30mm so I could not see that ;-)

I'd keep both if I could afford it. 24-105 is a great walkaround lens on a full frame body, but 24mm isn't really all that wide, besides the distortion at the wide end is rather atrocious. Really screws up any shots that have horizon in them.

In general I find 24-105 for stock to be average. It sure is convenient but the 21MP really shows it's faults.

If you can afford it, I say keep it.

Definitely.  Especially if you have a good copy of the 17-40. 

There seems to be pretty wide variation in quality from copy to copy of that lens.  Lots of folks at dpreview.com (including me) have complained of soft copies. 

If you have a good one hang on to it!

I am not sure if I got "good" or "soft" copy. I was thinking that now with 5Dmk2 I should calibrate it anyway with micro adjustments camera gives me.

If it has been your main lens and you are getting sharp pictures you got a good one.  If it looks like you took every photo through a soft filter or a dollop of vaseline you got one like mine

FWIW I have been shooting with the 5DII since December 08 and haven't had to have any lenses calibrated to work with it.  They all work fine.