Working Holiday Visa Expired-Staying longer in the UK

My working holiday visa will expire very soon. I was wondering if I can stay in the UK for a few more weeks to travel within the UK. I know I can't leave and come back without going back to Canada first. But I've heard that if I stay longer than my visa, I may have trouble entering the UK in the future cause I may be listed as a "over-stayer". Any advise from someone who stayed longer than their visa??? Please help