One 11-ounce can mandarin oranges in light syrup, drained well
One 10-ounce jar maraschino cherries, stems removed and halved
Position an oven rack in the center of the oven and preheat to 350 degrees F.
Spread the pecans on a small baking sheet and bake, stirring once halfway through, until lightly browned and toasted, 6 to 8 minutes. Transfer the pecans to a medium bowl and cool completely.
Whip the heavy cream in a medium bowl with an electric mixer to stiff peaks. Stir in the sour cream by hand until combined. Stir in the marshmallows, pineapple and coconut. Gently fold in the mandarin oranges. Cover with plastic wrap and refrigerate until chilled, at least 2 hours and up to overnight.
Right before serving, roughly chop the pecans. Fold the pecans and maraschino cherries into the ambrosia salad. Transfer to a serving bowl and serve immediately.