I'm thinking of some French Christmas carols, which would work wonderful with a marching band (I'm a Band Director in public school), provided they have a strong percussion section. The First Noel wouldn't work with marching band One or two lyrical French numbers would work well, too, provided the band is still (not marching) when playing those lyrical pieces.

Go to www.jwpepper.com and see what they have. I get almost all my band arrangements from there. They have a section for religious Christmas Band arrangements. As the French are mostly Catholic, they won't have a problem with you playing some version of a French Christmas carol with religious meanings. Some of your audience might even sing along!

They would LOVE you for playing their music, something they can relate to!