Cathy, you will find the schedule in French of Notre-Dame Easter services at
http://notredamedeparis.fr/index.php?page=calendrier&date=2008-3-23&id_rubrique=1. You should be there 30 minutes in advance minimum (hard to predict). In general, many Paris attractions and restaurants will be open. Pay attention. Restaurants are often closed Sunday night anyway. You can check attractions by browsing through Paris Digest and following links to the respective web sites. Have a great stay in Paris.