As a 7D user (and 40D before that), I have to agree with the people who've already cautioned against the 24-105. I'm sure it's an excellent lens, but the question is whether it would be a good focal length range for you on APS-C. For years I had a 24-70 2.8 (Sigma in my case) because I thought I'd move to a 35mm sensor camera "one day". I was pretty happy with the IQ (and Canon was too expensive for me), but I just didn't find it a very useful focal length range. I often wanted either wider or longer, so I carried a 10-20 f3.5 and 70-200 f4 as well ... and I found myself using the 24-70 less and less. And I also found myself often using the 10-20 but wishing it was a little bit longer, or using the 24-70 and wishing it could go wider ... or doing a LOT of lens swapping.
I keep thinking I'll move into a full frame but, truth be told, it gets more doubtful as I age. For that reason I haven't spent a lot on EF-S glass but all the praise the 17-55 is getting sure impresses me.
In your case, I think the first question is whether you'll be happy with the IQ of a super-zoom and can live with the relatively small max aperture. My brother has 18-200 and it's not bad in good light and excluding the ends of its range. If you want better IQ, the 15-85 is worth considering (my sister really likes hers) but there is still the question of whether the max aperture is enough. The 17-55 is obviously an option although the range is less, or perhaps the 15-85 plus something like the 28 f1.8 for the evenings/indoors (and when you want a more compact kit eg wandering around the streets)? Or your Tokina, a 28 f1.8 (or similar, maybe 35 f2?), plus something longer? For something longer, the 55-250 must be worth a considering if you're looking for small and light (I haven't use one so can't really comment). Or there is always the 70-200 f/4 - at least it's smaller than your 2.8!
If I look at this trip realistically, which is hard for me, I doubt I will be needing any long lens for shooting. The wide-angle end is probably more important. Sootzzs might give more insight into that area since he has been there. The super-zoom category has always concerned me in the IQ. Most reviews mention good IQ between x and y but not on either end. They usually have some sort of disclaimer that says, in effect, "this is a great lens, for what it is." My 70-200 2.8L has probably spoiled me for IQ.
Of course, so much depends on what you want to shoot / what focal lengths are important to you. If 24-105 covers the focal lengths you want to use, I'm sure you'd be happy with it.
No doubt it is a good lens and would probably fit well in my kit but it probably isn't the best choice for this particular trip.
Lastly, the mirrorless idea (OM-D maybe??) has got to be worth thinking about. I'm sticking with my 7D for now (largely because I like to shoot action sometimes) but the size/weight of the mirrorless stuff makes it tempting!The size and weight of mirrorless is certainly a consideration but since I usually shoot wildlife, birds, great-grandkids (who may fit in the first category), and kids sports, they probably aren't my #1 consideration. I may break my prejudice about buying EF-S lenses and pull the trigger on the 17-55 2.8 IS when my photo-fund gets rebuilt.
Good luck with whatever you decide!
Thanks for everyone's input.