I guess, I have an answer for you...
Go for it... but, make a strong case that your cancer was eliminated 4.5 years back. some cancers today are curable and they ma consider.
Get tests done in advance showing no signs of cancer with your file. send a cover note to CIC Sydney along with Xerox of fresh reports. If they accept your case, then, send original reports to you local CHC along with your file.
In most likelihood, if your cancer is truly eliminated, they will consider.
They may ask for a few extra tests from some lab approved by them during the medicals phase.
Overall, the canadian immigration process is quite reasonable. I'm sure they'll oblige.