I would definately pick up a wide fast prime to take. There are many of the old cathedrals do not allow flash photography and you'll want one for those.
A wide prime is so small and light that taking one is a no brainer. And consumer grade primes offer image quality equivelent to L grade zooms at very a reasonable price. The Canon EF 35mm f/2 Wide Angle Lens is lower priced and gets better reviews than the EF 28mm f/1.8.
edit: I agree the 70-200mm f/2.8 is a lot of weight to be carrying around all the time, and a lot of money to leave sitting in a hotel room.
I still think you can't beat the Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens for image quality per dollar on an APS-C camera.
I'd take the Sigma 17-70mm for its extra wide capability, and buy a Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens (you can find new ones cheap from people who sell them on ebay, simply because they are kit lenses and they don't know better), and a Canon EF 35mm f/2 Wide Angle Lens.
That gives you a good focal range, good image quality, and good low light capability at a reasonable cost.
Sell the lenses that don't give you the image quality. KEH.com, bhphotovideo.com, and adorama.com all deal in used equipment. Or if you want to be more involved of course there is ebay, craigslist, or start an Amazon sellers account.
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