The main competitor of the Panama Canal is the Suez Canal. Because of the world's geoid shape a transport ship from New York can go to Hong Kong via Panama or Egypt in roughly the same amount of time.
Another reason for enlarging the Panama Canal is Nicaragua. Nicaragua will soon announce their plans to construct a super, sea-level canal. This is a bit ironic because before the United States liberated Panama from Columbia the original plans for ocean-to-ocean canal was a Nicaragua Canal.
In a "good thing that never happened side note," in the early 20th century the president of Nicaragua wanted Germany and Japan to operate a canal through his country. Something about a Central Power then Axis Powers having operation bases in the Western Hemisphere
rubs me the wrong way.