From what I have read it isn't. Here is what the Health Canada website says:
The Public Health Agency of Canada (PHAC) does not monitor cases of scarlet fever because it is not an invasive infection. An invasive infection is one where bacteria infect a part of the body not normally infected by bacteria, such as the bloodstream, muscles, and joints.

PHAC recommends frequent use of personal hygiene measures to prevent the spread of infection, and advises seeking medical attention as needed.



I haven't checked the Ontario health website.