Pour the apple juice or pear nectar into a medium saucepan. For spice bag, place the stick cinnamon, vanilla bean (if using), and cardamom on a double-thick, 6-inch-square piece of 100%-cotton cheesecloth. Bring up corners; tie with string. Add spice bag to juice. Bring to boiling; reduce heat. Cover and simmer for 5 minutes. Remove from heat. Cool and refrigerate at least 4 hours or until thoroughly chilled.
Before serving, remove spice bag and discard. Pour juice into a large pitcher or punch bowl. Stir in vanilla extract (if using) and the champagne or carbonated water. Add apples or pears and cranberries, if desired. Add ice just before serving. Makes 14 (4-ounce) servings.