I could see it being Washington DC or NYC. The only clue I would go off of is the look of the V/Five. And considering how cheap politicians are it could be Washington, or it could be possibly a hint at Wall Street.
Either way, not too interested unless there is a major overhaul on the game. No more damn escort missions. Ugh.
Why not Europe, haven't been there since like...GTA London.
I never played the first Just Cause but I had hours of fun playing the second one.
It is entirely more goofy and less realistic than GTA, also it is a bit retarded how some of the bosses can take about a hundred or more rounds of ammo point blank in the face before dying.
Vice City or Las Venturas seem likely but I would really love if they had the balls to go overseas, do the UK, South Africa or something similar.
I doubt they would ever set it in a place that isn't predominantly English as it would take away from the realism they strive for.