A second mortgage in Toronto is exactly that: another mortgage on top of your existing one. It allows you to borrow the equity from your home without refinancing. The loan amount available would depend on how much equity is available in the property. Due to the higher risk, private lenders will offer high interest rates (12-14%) and fees for the services.
Second mortgages are normally for those who have lower credit scores, income confirmation or those who need short term loans. They are usually for a 12 month term with the option to extend the loan. Monthly mortgage payments are based on interest only (no principal payment) which makes it more affordable.