Drain 2 (1lb. 14oz.) cans sliced pineapple; reserve syrup. Combine 2c. sugar, ½c. light corn syrup and 1⅔c. pineapple syrup in a heavy 10" skillet. Cook over medium heat, stirring constantly, until mixture boils. Cook until temperature reaches 234° on candy thermometer.
Add a third of the pineapple slices; bring to a boil. Reduce heat; simmer 25 minutes or until pineapple is transparent around edges. Remove from skillet; drain on wire rack. Repeat with remaining pineapple, cooking a third at a time. Then add 3 (8 oz.) jars maraschino cherries, drained. Simmer for 25 minutes. Let dry 24 hours at room temperature.