Why canals did not compensate for China's weak navy

Could China's Grand Canal have given its navy an advantage against foreign fleets?

Only with a capable navy; in the Opium Wars the waterways instead helped British ships bring firepower against Chinese cities.

China's canals offered routes for moving vessels and supplies, but infrastructure alone could not create maritime combat power. Effective use against Japan or another naval enemy required a competent Chinese fleet. During the Opium Wars, the Royal Navy instead exploited inland access by sending heavy warships close enough to threaten cities. The example separates transport geography from the institutions and ships needed to turn that geography into an advantage.