MedlinePlus is a good place to start. It provides health information from the US National Library of Medicine and National Institute of Health with easy access to Medline and health topics, medical dictionaries, directories and publications. It can give you:

• overview of the disease/condition
• symptoms & diagnoses
• treatment
• images & videos (sometimes)
• disease management
• links to U.S. cancer agencies
• links to related research

UpToDate Patient Information

• articles written according to latest information by physicians who are experts in their field
• updated based on new medicla findings
• reviewed by multiple experts for accuracy

In addition to the websites listed, also search for specific cancer websites such as Prostate Cancer Canada, Canadian Breast Cancer Foundation, Leukemia & Lymphoma Society of Canada, etc.