This year marks the 70th birthday of the world's biggest film festival, with A-listers including Nicole Kidman, Clint Eastwood and Will Smith set to grace the glitzy French resort amid "unprecedented" tight security.
Miramax supremos Bob and Harvey Weinstein were due to officially announce their backing in Cannes of the new documentary from leftist provocateur Moore, billed as an expose of the US leader.
In "Fahrenheit 11/9" -- a nod to the date Trump was elected, as well as Moore's "Fahrenheit 9/11" that won the Palme d'Or in 2004 and smashed box-office records -- Moore has pledged to take down a president who has so far managed to survive an avalanche of scandals and controversies.
"Facts, reality, brains cannot defeat him. Even when he commits a self-inflicted wound, he gets up the next morning and keeps going and tweeting," Moore said in a statement quoted by Screen International magazine.
"That all ends with this movie."
Italian star Monica Bellucci is set to host Cannes's opening ceremony on Wednesday night, with French drama "Ismael's Ghosts", starring Marion Cotillard, as the opening film.
Spanish director Pedro Almodovar is leading the jury charged with picking a winner amongst the 19 films vying for the coveted Palme d'Or top prize, on a panel that also includes Smith, "Interstellar" star Jessica Chastain, and Chinese actress Fan Bingbing.
Stars are arriving under tighter security than in previous years, 10 months after the truck attack in nearby Nice killed 86 people.
Concrete barriers -- in the form of giant flower pots -- have been set up to try to block a similar assault, and snipers have been positioned above sensitive sites.
Patrick Mairesse, a top regional security official, said the goal was to be as "invisible as possible, to cause as little nuisance as possible -- so the party can stay a party."
