You might want to switch up controls.
Maybe make it so that instead of everything is drag controlled, make the cannon aim with the mouse, and the house be controlled with the arrow keys/WASD.
But good game overall.
You might want to speed up the amount of time it takes for more then one plane to start appearing, and a money system instead of a definate upgrade, but then again, that's your call, and with some tweaking, the definate upgrade system isn't a bad idea.