If i had a ct scan no contrast of bowel, would it show colon cancer?

No, this common CT technique which is usually done in acute abdominal conditions without time for preparation does not detect colon lesion. However, a different technique called CT colonography (virtual colonoscopy) can be used as a screening tool for colon cancer but you need bowel cleaning + drinking oral contrast for preparation + air insufflation per rectum just before the CT done.

Suboptimal for early phases, may suggest colon cancer if large enough, sometimes also revealing liver lesions that per further work up prove to be mets from colon/gi cancer.

Ct scan is not the ideal test for colon cancer- colonoscopy is