i like the suggestion of South America, mainly because in the original Gundam, the Federation H.Q. "Jaburo" is located there (and is always being infiltrated by that pesky Char, or about to have a space colony dropped on it by those rascally Zeons, or... ) but as others have suggested Japan is reasonably likely simply for the same reason "EarthGov", or "Star Fleet H.Q (No, The OTHER Star Fleet)", or "Central" is always somewhere in the U.S; it reflects the cultural bias of the series creators.
Good spot on the cherry trees! (which might not actually suggest Japan, though - again, cultural bias sometimes sneaks through to other settings; I recall seeing an anime once where a protagonist arriving in the U.K. by Eurostar train was bowed at upon arrival by the station staff... ).
"The power of bakers, the power of artists; even the power of witches! It must be a power given by God... sometimes we suffer for it."- Ursula, Kikis Delivery Service.