Hey Ken, first and foremost, Welcome to the forum. Super envious of your travel plans to the Glapagos as its one of those places I've always wanted to visit it myself
If I were going, it would be a no brainer to upgrade to the 5DMark II for a once in a lifetime trip like this and keep the Rebel as a back up body. This would give you you the best of both worlds as the 5D is full frame and will help with those real wide angles, and if you only bring the 24-105, I'd keep that on the Rebel because of the crop factor it would bump your 105mm up to 168mm and your 300mm up to 480mm without adding any extra f/stops, if you need that extra length to get close to wildlife.
With the 17-50 and the 24-105, I'd leave the 50mm at home since both those lenses cover that range. It would seem a bit redundant to have it taking up room in the camera bag.
One thing that I'd add to the arsenal would be either a waterproof housing or a waterproof bag like the ones Luca and I have talked about in past reviews.
Being as 90% of your shooting will be around water, I'd want those cameras protected from splashes, drops or heaven forbid getting dunked in the surf.
Being as you can get so close to most of the animals, unless you were trying to do real low light photography, I cant see the need in bringing a tripod either. And with the lens lineup you're bringing, I wouldnt really worry too much about a tripod, I'd figure everything will be hand held in good light.
With the new bodies amazing noise reduction, you can get away with bumping up your ISO to compensate for any low light photography you might incounter and not worry about degrading the images too much.
Another reason I could justify the 5DMark II would be the capability of video. This would lighten the load to not have to bring a video camera along, and many times when an animal is doing something really different, still images just dont capture the feeling right. Having the availability to throw a button and have video at your finger tips for an adventure like this would seriously move me towards the 5D MarkII
Plus with the 7D just being announced today, prices for the MarkII are going to keep coming down in the next coming months. Check out the buy/sell forums on Fred Miranda or POTN and snatch up a used MarkII body and call it good!
Make sure to post up some images when you return to make us all drool