which lens should I use for a wedding shoot?

It depends on what size sensor you have. For 35mm photography, something like a 35-85mm range is good for group shots and portraits. The second lens is usually something like 70-200 for candid shots. If you're using an APS-C sized sensor, then the 17-50 is good. You still need a telephoto. As an aside to Secular, I'd like to hear the explanation for why a Tamron lens will not last as long when used on a Canon camera.

I shot a wedding recently with the 28-70MM USM F2.8 on one camera and the 50MM F1.8 on the other camera (for details, rings, flowers, etc). I had one camera on each shoulder, otherwise it takes times to switch lenses and we miss the 'action'.

Don't use the kit lens as you will not be able to get a nice bokeh that the 85MM gives you

If you don't have the equipment find a local place to rent

Only a 85mm or 135mm at a wedding would be a disaster; they are both telephoto lenses. Ideal for portraits or altar shots, you will need wide for groups and a decent zoom for the variety of images you'll need to take. I usually wear two cameras, one with a fast prime and the other with a 28mm - 135 mm zoom.

85mm is nice fast lens tht'll work great in the lowlight ..so i guess it'll do just fine.. but still if u want why not carry the 135mm..but anycase why need to zoom unless its a huge room and the pavement on which the bride-groom are standin is too far etc..

Without knowing exactly what you are trying to do, i can only give an opinion of what works for most anything. The Canon EF 70-200mm IS II 2.8L happens to be my favorite. It is expensive though but if you're that much of a photography buff then its worth it.

You need a selection of lenses and it would best to have a spare camera also in case of a failure of the first one. You should scout the location to get an idea of the light levels and the area you will need to include in some of your frames. I hope you aren't the PRIMARY photographer for this wedding. Without knowing EXACTLY what you are doing, you stand a good chance of making enemies out of the bride and groom.

I don't want to repeat the other answers, so i'll just post the usual link:

http://www.rokkorfiles.com/Wedding101-page1.html

Read it carefully. Note that there are more pages to this article, the link to them is at the very bottom and easy to miss.

85mm should be fine