Owing to good high ISO performance (I'm uncertain about the 7D), you could /possibly/ get away with the 400mm f/5.6L.
I'm kind of edging towards the 300mm f/4L IS USM and taking your Extender 1.4x with you.
You just need to bear in mind that you're likely going to be shooting animals in the wild. You need aperture to be able to freeze the moment, as you can't expect wild animals to sit still.
Are you able to rent any 2.8L lenses and go overseas with them? I just feel that with smaller apertures, you might struggle a little.
My 0.02c.
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