I recently had a request from a bride to do the same thing: play along with a DJ’s recording. She thought the harp wouldn’t be enough on its own. To my knowledge there are no CDs made for this type thing (other than those you play along with to learn to improvise in jazz) and it would be a major hassle. You need to be able to edit a processional as you play it so the music can be adjusted to fit the time it takes the bride (or whoever) to cover the distance from point A to point B. This is never exactly the same no matter how many times it’s done. Tying yourself to a recording defeats the purpose of having a live musician (the flexibility of timing). You need to explain to her (nicely!) that this is unnecessary and impractical. I’m sure when she hears you play the Canon, she will realize you sound wonderful and complete with no accompaniment.