Your planetary ruler is the Moon, notwithstanding the fact it’s not technically a planet. Moon is a celestial body that is the closest one to the Earth and this fact can’t but reflect the nature of stay-at-home Cancerians who love spending time with their close ones more than anything else.
Besides, the Moon rules your emotions and is the planet responsible for the personal growth. Cancer people have hard shells yet soft underbellies and have to give much attention to their inner world as well. They’re sensitive and value personal care, and these qualities are inspired by the Moon, too.