Hello Amit!

I had some plans also to visit Antarctica and the South Georgia.
I would of course wish to first have the full frame DSLR.

I have the EF 8-15mm fisheye which is very light and small to have with you on the trip. However remember that the angle of view is as best for FF @ about 14mm of focal lengt in the "tele-end" of this lens AND you need to hold it absolutely in spirit-level in order to NOT have your landscape lines curved.
I use a spirit-level on the flash-shoe.
I think I could either take my EF14mm f/2.8L II (rather fast and have auto-focus) or my TS-E 17mm f/4L but on these harsh conditions of weather I would still prefer not a manually handled wide-angle lens such as TS-E with cold fingers and salt-water-waves breaking in to the Zodiac boats.

I think a 70-200mm f/2.8L II with both new Extenders could make a good job.
Also the new EF300mm f/2.8L II with the Extenders will be handheld and give you extraordinary IQ of wildlife and also landscapes from the boat and BIF!
I think the EF16-35 II would also be quite versatility lens or the new EF 24-70mm f/2.8L II with better weather sealing and flourine shielded surfaces as also the new fish-eye have and the EF300 f/2.8L.

So in the end - please consider WHAT you wish to capture mostly - the dramatic landscapes and skyscapes or mostly the birds and wildlife? For landscapes you need really wide-angel lenses - yes the 17-40 sounds good but what if there is low-light conditions and you might need the EF16-35 2.8L II?
The fish-eye can be versatile BUT it can also be a bit too much if you use it for plenty of photos - you might need two bodies - one FF equipped with wide-angle and the other with tele-lens like 70-200mm.
Think about that you need rather mobility and to be fast moving on land when you stay just for a short time in different places and then hand held with good IS is to prefer as well as a fast lens!

In the end YOU have to decide WHAT is the MOST IMPORTANT memories you wish to bring home with you after a life-time-memorable trip to Antarctica!
What ever you choose - your photos will be stunning!
Wishing you all the very best and wonderful travel to the true wilderness and the almost much un-known and a bit hidden and unique continent of Antarctica!

//Charl