Can a colonoscopy help detect prostate cancer like from bulging?

No. Bulging prostate may have nothing to do with prostate cancer. Stick with a finger examination and psa testing.
Not Common Technique. The colonoscopy in itself may not visualize an enlarged prostate, in more advanced cases the prostate cancer can erode through the rectal wall and appear like a rectal cancer. Prior to inserting the colonoscope the gastroenterologist performs a digital rectal exam in which he might feel abnormalities of the prostate. A prostate abnormality does not necessarily mean cancer but should require eval.