Go to
www.cpso.on.ca which is the web site for the Ontario College of Physicians and Surgeons and do a Doctor Serach. If you do an Advanced Search, you can identify certain characterisitics of the doctor you are looking for, one of which is those accepting new patients.
In my opinion your best choices are University Hospital Network Princess Margaret or Sunnybrook for cancer care. And both have excellent reputations.
I did a quick search and found Dr. Pam Goodwin at Mt Sinai which is part of UHN and Princess Margaret is accepting new patients. I know she has very well thought of, but I have never consulted her myself.
PMH is right down town and very accessible. Sunnybrook is just in the near north east end of the city and also pretty handy.
Good luck.