The two Sui emperors fixed this problem with an inland waterway connecting north and south. The Grand Canal still exists and still performs the function for which it was built. Calling it a canal, though, sort of trivializes it. What the Sui dynasty emperors did was carve a major artificial river into the earth, connecting their two enormous natural ones, the Huang He and the Yangtse. The Grand Canal provided a safe, placid, entirely defensible, and controllable waterway, up and down which barges loaded with grain could float.
