Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9×13-inch baking pan.
Beat white sugar and eggs together in a large bowl until smooth; mix in coffee. Whisk flour, baking soda, cinnamon, and salt in a separate bowl. Beat the dry ingredients into the moist ingredients just until combined; stir rhubarb and strawberries into the batter. Pour batter into prepared cake pan and sprinkle top with brown sugar and pecans.
Bake in the preheated oven until the cake is lightly browned and a toothpick inserted into the middle comes out clean, 45 to 50 minutes.