Pour whipping cream into a large bowl and whisk until soft peaks begin to form. Slowly add confectioner's sugar and vanilla and whip until stiff peaks form. Fold in oranges, grapefruit, pineapple, coconut, marshmallows and roasted pecans. Pour into a large glass bowl. Wrap tightly with plastic wrap and refrigerate for about 8 hours before serving. When ready to serve, add cherries to top of ambrosia and serve.