You should open it. It will make your life so much easier.

Carry on the unit itself, and put it through the x-ray.
Check the packaging (put it in your checked bag), and reassemble the package when you reach your destination. The "factory" seal is just a strip of clear tape, so your recipient probably won't know the difference. Even if they do...who's going to complain that the brand-new PS3 they received as a gift was missing a strip of tape on the box?