Can I have a Buddhist prayer said in my Catholic wedding?

I’m sorry to tell you that this is not allowed. Catholic prayers are said at Catholic weddings; Buddhist prayers are said at Buddhist weddings.

The principle here is that one should always avoid the practice of “syncretism”; that is, the combination of the rites and prayers of various religious traditions into an amalgam which is truly expressive of none of them. Granted, there are some quite beautiful prayers in other religious traditions. At first glance it may seem like a good idea to try to include one in your ceremony. But experience has shown that it just doesn’t work. Trust me on this one. I’ve seen it tried.

Instead, use the very beautiful prayers that are already included in the Rite of Christian Marriage. There are many options for the various prayers which are said during the rite. Spend a lot of time going over them with the priest or deacon who will be performing the ceremony. You will be glad you did.