Once you've recovered, you have options regarding your employment.
About 10 per cent of workers are covered by federal labour legislation (including people working in banking, interprovincial transport, broadcasting, etc.). Everyone else is covered by provincial laws, which vary widely. Find out about the labour or employment standards in your province. Many workers are also covered by collective agreements that are often superior to any provincial or federal provisions. If this includes you, speak to your union representative. Finally, employers themselves may provide special consideration to those with serious illnesses, even if the policy is not itemized in the company rules and regulations.
Willow support services has a publication called Coping With Your Financial Concerns When You Have Breast Cancer
Cancer and Careers, Living and Working with Cancer offers tips on situations such as how to handle work demands during illness and telling co-workers you have cancer.
Princess Margaret Hospital in Toronto has a PDF guide called Getting Back on Track: Life After Treatment