Their fizzy Gugar soda, in flavors such as tamarind, grapefruit and tangerine, is cheaper than brand-name sodas and caters to the area's poorer residents.In the company's plant, as pineapple sodas whirred by on conveyor belts, the face of the third generation, 29-year-old Juan Pablo Guzman, Mario's son, walked into a side storeroom and pointed at piles of 200-pound white sacks of sugar. ???This is