Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking dish.
Mix flour, 3/4 cup brown sugar, baking soda, and salt together in a bowl. Mix in sour cream, honey, and vanilla extract until thoroughly blended. Mix in eggs until just blended. Fold rhubarb into the batter.
Spread batter evenly in the prepared baking dish.
Mix 1/2 cup brown sugar, white sugar, pecans, and cinnamon together in a bowl. Stir in butter until mixture starts to clump together. Sprinkle mixture over batter.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 45 minutes.