As a general rule of thumb, participation in the religious rituals of the nuptial liturgy or Mass (e.g., the readings, distributing Communion, altar service) should be reserved to practicing Catholics. Participation in the social customs common to most American weddings (e.g., bridesmaids, groomsmen, ushers) can be offered to anyone, Catholic or non-Catholic. One exception might be bringing up the gifts during the Offeratory, which can be done by anyone, but if there is a possibility of confusion over the matter among your relatives and friends, it might be prudent to choose practicing Catholics for that task as well.
