Preheat the oven to 350°F. Spread the pecans on a sheet pan in a single layer. Toast for 6-8 minutes or just until fragrant and lightly golden. Set aside to cool.
Cake: Spray a 13x9-inch cake pan with baking spray. Set aside.
In a large bowl use an electric mixer on medium-high speed to beat together the cake mix, pudding mix, flour, buttermilk, butter and eggs until fully combine. Pour evenly into pan.
Bake for 25-30 minutes or just until a toothpick inserted into the center comes back clean. Use a fork to poke holes all over the cake. (Be generous.) Let cool slightly while you make the pineapple.
Meanwhile, bring pineapple with juices and 1/2 cup sugar to a boil in a small saucepan, stirring occasionally. Boil just until the sugar is fully dissolved, about 2 minutes.
Spoon pineapple mixture evenly over the cake. Let the cake cool completely in the pan.
Frosting: In a a large bowl use an electric mixer to cream together the cream cheese and butter.
Add the powdered sugar one cup at a time beating well after each addition. Add the vanilla, beating to combine
Frost the top of the cooled cake and sprinkle with toasted pecans.
Chill thoroughly until serving garnished with maraschino cherries, if desired.