when in doubt just give whatever information you have of ANY medical problem that you have. And then let IRCC decide.No matter how people try to justify how to answer this question cancer IS a serious disease, anything that puts your body through the stress of radiation or chemo is serious, you can do whatever you want with your application, but I would advice strongly against hiding this, Canada is a honour system and if found out that you lied in your application, the consequences will be worse, I don't think they will reject you at this stage but of course all the details of your father's disease should be detailed in the report that the panel physician sends with the medical test
Just so you are ready, get a letter from the Oncologist indicating the prognosis of your father, that he was treated for X type of cancer, that he is cancer free and he is stable and that there are no indications that he could relapse. Have this letter ready for when you get the medical test and the doctor can attach it to the exam, it's entirely up to the Canadian authorities to determine if it's an excessive demand on the medical system here, not up to you or what people say here
Having said that some of us have experience with treating patients and even doing these medical examinations for immigration and employment purposes and know what conditions are typically what the organizations are looking out for.