Drain the canned fruit: pour the mandarin oranges, pineapple tidbits, and maraschino cherries into a colander and let drain for about 1 hour. After draining, gently pat the fruit dry with paper towels to remove excess liquid.
In a medium bowl, combine the 3/4 cup heavy cream, 1/4 cup powdered sugar, and 1/2 teaspoon vanilla extract. Using an electric mixer on high speed, whip until stiff peaks form.
Add the 1/2 cup sour cream to the whipped cream and gently fold or stir until the mixture is smooth and evenly combined.
In a large bowl, combine the 4 cups mini marshmallows and 1 1/2 cups sweetened shredded coconut.
Add the well-drained mandarin oranges, 1 cup pineapple tidbits, and 3/4 cup maraschino cherries to the marshmallow–coconut mixture.
Chop the 1/2 cup nuts into small, bite-sized pieces and add them to the bowl.
Pour the whipped cream and sour cream mixture over the fruit, marshmallows, coconut, and nuts. Gently fold everything together until all ingredients are evenly coated.
Cover the bowl and refrigerate the salad for at least 1 hour before serving.