If i've been told there's a pretty good chance i have colon cancer would that be the reason when i go to the restroom that my legs always go numb?

Maybe: First off, if you've been told you probably have colon cancer, check it out right away, get treated. Numbness after going to the restroom suggests you are sitting in one position too long. This can occur if you have a partial blockage from a cancer which makes it hard to eliminate the feces. It could also be totally unrelated perhaps some spinal problem. As always, let your physician evaluate.