Preparations have been underway for a year for what is being billed as the biggest international summit ever hosted by France, to be attended by 8,500 delegates and journalists who will clock up 35,000 hotel nights.
Locals have their ideas about which luxury hotel will be hosting the likes of US President Barack Obama -- the Carlton? -- but officials are tight-lipped about where leaders will stay for security reasons.
Cannes' famous Croisette seafront will be off limits to anybody except delegates and inhabitants with a security pass, while a section of the town centre has also been cut off to outsiders.
Around 12,000 security forces and police are being brought in from around France, and some schools have even put back the return to class from the mid-term break to after the summit has finished.
A police official said that snipers would be placed on rooftops overlooking the routes taken by the heads of state and government from the world's 20 biggest economies during the summit on Thursday and Friday.
In Nice, around 30 kilometres (20 miles) down the Mediterranean coast, 2,500 extra police have been drafted in to deal with anti-globalisation protests set for Tuesday that organisers hope will be attended by 10,000.
But anyone thought to be associated with the so-called Black Bloc militant protests faces arrest if police find them anywhere in the region.
"The worst thing would be for things to go badly and for their message not to be heard," Nice mayor Christian Estrosi said of NGOs' hopes that their message would not be overshadowed by violence.
Estrosi said that President Nicolas Sarkozy would host NGO representatives in Paris already on Wednesday.
Events in Nice are being billed as a "people's summit", running from the day of the main demonstration on Tuesday to the end of the summit on Friday.
The events are expected to draw large numbers of people particularly from Italy, Germany and Spain.
Besides the police presence, organisers will have one person out for every 100 demonstrators, or around 100 in total.
An abattoir in Nice turned cultural centre will host speeches, a concert and an evening dinner on Tuesday.
On Thursday, some protesters will head to the principality of Monaco to "celebrate" the end of tax havens that had been announced at the 2009 G20 in London.
Franck Gaye, one of the organisers of events in Nice, is hoping to get locals to take part in debates and have handed out flyers to try to reassure fearful shop-owners.
"There will be no attempt at confrontation at the G20 summit, which is happening somewhere else, on another day," said Gaye, noting that anarchist movements "have called to go everywhere in France because there won't be security forces elsewhere."