I was thinking about making a airplane (2D) out of foam board and mounting 1 computer case fan (25cfm each) on the top of each wing. Would this have enough power to keep it in flight?

Dunno

I.T. should be enough as long as you make the plane the right size for the motors.

I saw a thread a few years ago where a guy did just that. H emade a "Delta" for the wing and taped another triangle below it at right angles for the fuselage - sortof looked like a papre plane.

He used 2 channels on his radio - one for the rudder (which being mounted below the fuse meant it induced rol in the right direction as if he was using aileron) and elevator.