Place cubed pork, cubed chicken and shrimp in a large bowl, and season with salt, sugar, and soy sauce. Mix in the egg white and green onions. Cover, and place in the refrigerator at least 1 hour.
Heat oil to 365°F (185°C) in a large, heavy saucepan or deep fryer.
Coat the pork with cornstarch, and fry in the heated oil about 10 minutes, until evenly browned. Drain on paper towels.
Heat oil in a wok over medium heat. Stir in the celery, green bell pepper, and onion, and cook until tender. Season with salt and sugar. Remove from heat, and set aside.
In a large saucepan, water, salt, sugar, apple cider vinegar, ketchup, and soy sauce. Bring to a boil, and stir in the cooked pork mixture, celery mixture, and the pineapple chunks with juice. Return to boil, and mix in cornstarch and water to thicken. Cook until well blended.