Thanks everyone. As suggested, I am kicking around the idea of the EF 16-35 f/4. A rental price of $95 for 2 weeks would give me some time to test it out before the trip, and, of course, it is on the "next tier" of lenses I have in the back of my head that I might like to buy. I could see the IS and UWA being a good combination inside cathedrals and for quick landscape shots. Plus, it is 77 mm thread, which I already have.

I thought about TS-E lenses, but I think that is a skill I would want to develop before going to someplace like London/Paris. Then, if the EF 11-24 is even available, I don't even need to check my bank account. Plus, how many shots with my toes at the bottom do I really need?

I appreciate the advice on the 70-200. It is along the lines of what I have found. When I travel with it, but it either gets used a lot or not at all. It is to the point where I am not going to automatically travel with it, but, after scrolling through Flickr, I found a number of shots I may want to make were at 200 mm (here, and here). I'll think about it a bit more, but it will likely still make the cut.