Monte Carlo (the City), is in the Principality of Monaco. Whilst it is a sovereign state, it is a protectorate of France.
There are no airports there, just a couple of heliports. No flight plan is required to cross into Monaco because it lies within French airspace. A flight plan is required if you intend to fly any distance out to sea though, under French flight-plan rules for VFR flights.
From the air, the view is OK, but brief, the place is tiny and centred around a single Bay overlooking the sea.
Overflight of the city is not encouraged.
Cannes to Monaco is around an hour's drive on the Autoroute. Nice is a much closer airport than Cannes, but it costs an arm and a leg for GA to land there.
There are nicer places in that neck of the woods than Monaco IMHO
2D