I had my medical exam in August 2020 and, beforehand, I contacted my family physician, as well as all the hospitals where I have had my follow-ups throughout the years, in order to request any letters/correspondence they might have regarding my case. In the end, I managed to obtain about 5-6 letters referring to my follow-up results and next steps. I took all these letters to my medical exam, but the physician was only interested in the very last one, which he took a scan of and uploaded to my online record.
I heard from IRCC 3 weeks after my application was submitted, to say that my medicals have been passed
I think it’s important to be truthful (there is a question on the application form asking if you’ve ever suffered from a serious disease, so it’s practically impossible to keep this from them without lying) and make sure you have paperwork from your doctors to support the information you are giving. If you do not have any paperwork, IRCC will ask for it, so best to have it from the beginning.
There is no illness that would automatically make you inadmissible, it’s all on a case by case basis. If your prognosis is good and you can prove it, it’s unlikely they will reject you.