Opposition figurehead Sam Rainsy, who lives in exile, has alleged that the project would serve the interests of China.
The waterway is part of Beijing’s huge Belt and Road Initiative, a massive infrastructure scheme across Asia, but Hun Manet insisted it will only serve Cambodia.
“(We) do it within the Cambodian territory for the Cambodian people and for the interest of Cambodia,” he said.
“We will have a groundbreaking ceremony this August.”
The canal – 100m wide and 5.4m deep – will connect Phnom Penh with Cambodian ports on the Gulf of Thailand.
Cambodia and China also wrapped up their largest annual military exercises on Thursday, involving several Chinese warships and hundreds of Chinese military personnel.
In December, two Chinese warships made a first visit to a Cambodian naval base that the United States says could be used to boost China’s influence in the Gulf of Thailand.
Cambodian officials have repeatedly denied that the base, near the port city of Sihanoukville, is for use by any foreign power.
US Defence Secretary Lloyd Austin is set to visit Cambodia on Tuesday.
