May I suggest some around to a billion total pop or something in the hundreds of millions, if the numbers must be high. High enough to be big, but not crazy huge.

And here's my suggested land borders for your nation.
[hider=Click][img]http://i136.photobucket.com/albums/q173/sigma830/Map1_zpsymt0mllz.png[/img][/hider]
Big enough to warrant superpower status, and but not so huge that it eats up most of the continent.