Preheat oven to 350 degrees F (175 degrees C). Grease one 9x5 inch loaf pan.
In a small saucepan, combine the raisins and the rum. Cook over medium heat until simmering, then remove from the heat and allow to cool 10 minutes.
In a large bowl, mix together the mashed bananas, brown sugar, canola oil, and eggs with an electric mixer for 1 minute. Sift together the all-purpose flour, whole wheat flour, baking powder, baking soda, salt, and ground cardamom; stir into the egg mixture with a spoon until well blended, Stir in the walnuts and the rum soaked raisins last. Pour the batter into the prepared pan.
Bake in the preheated oven for 50 to 60 minutes, or until a toothpick inserted comes out clean. Allow bread to cool slightly before removing from the pan.