Preheat oven to 350 degrees F (175 degrees C). Grease a 9x9 inch baking pan.
In a large mixing bowl resift flour with the baking powder, baking soda, salt and 3/4 cup of sugar. In a separate bowl combine the egg replacer and water (2 eggs' worth) and mix in sour cream substitute and vanilla. Pour the 'egg' mixture into the flour mixture and beat until smooth. Spread batter in baking pan. Sprinkle blueberries (optional) and/or walnuts (optional) over the batter, and stir slightly so that they stay in the top layer.
In a small bowl, combine the 5 tablespoons sugar, margarine and cinnamon. Mix with a fork until mixture resembles cornmeal (not smooth). Sprinkle topping over batter.
Bake in preheated oven for 20 to 25 minutes, or until a toothpick inserted into the center of the cake comes out clean. Cool slightly before serving.