Heat the water and sugar in a small pan, until the sugar is totally dissolved. Stir in the Grand Marnier, and remove from the heat. Cool to room temperature, and set aside.
Cake
Grease a 9-inch springform or 10-inch tube pan, and line with parchment paper. Preheat oven to 300 degrees.
Combine pecans, cranberries, pineapple and red cherries in a large mixing bowl. Whisk together sugar, flour, baking powder, nutmeg and salt in a medium bowl, and add to the fruit. Toss to coat. Stir in eggs and vanilla until combined.
Set batter aside to rest for 30 minutes.
Give the batter a good mix, and then pour into your prepared pan. Press evenly into the pan. Bake about 1½ hours until set, and the top of the cake looks dry and is just starting to turn golden brown. When the cakes is done, transfer to a cooling rack. Let stand for five minutes, then run a sharp knife around the edge and then release springform.
While the cake is still warm, brush with syrup (before brushing with syrup, you can decorate the top with more whole nuts and cherries if desired). Let cool 30 minutes, then spoon additional rum or bourbon on top, if desired.
When completely cool, remove the cake from the pan base, and peel off the parchment paper on bottom.
If not eating right away, wrap fruitcakes in plastic wrap. Fruitcake will keep for two months in the refrigerator. If storing, sprinkle with more alcohol an hour before serving.