Have any suggestions for my Canon T2I?

I normally shoot Nikon for work, but I've got this T2I lying around and a friend of mine asked me to shoot some wedding rehearsal pictures. The church has high white ceilings and stained glass windows. There's a lot of natural lighting. Any suggestions for settings? Is there anything I should be thinking about when I'm shooting?

If your friend doesn't mind flash do it that way.

If flash is an issue get a 50mm f/1.8 lens and work your ISO to get the best results with natural lighting.
I would also go to the church, using which ever - new lens or flash, and a model. Shoot some test photos at the same time of day when the rehearsal will be and see what happens. You might also go over your test results with your friend to see which works for him / her.