Hi,
This is from the Infectious Disease Emergency Leave, Section 9 
“Proof of entitlement
An employer may require an employee to provide evidence reasonable in the circumstances at a time that is reasonable in the circumstances that the employee is eligible for unpaid infectious disease emergency leave and/or paid infectious disease emergency leave. However, employers cannot require an employee to provide a certificate from a physician or nurse as evidence. Employers are not prohibited under the ESA from requiring medical notes in the context of issues such as return-to-work situations or for accommodation purposes.
What is considered reasonable in the circumstances will depend on all the facts of the situation, such as:

• the duration of the leave
• whether there is a pattern of absences
• whether any evidence is available and the cost of the evidence

If it is reasonable in the circumstances, evidence may take many forms, such as:

• a copy of the information issued to the public by a public health official advising of quarantine or isolation (for example, a print out, screen shot or recording of the information)
• a copy of an order to isolate that was issued to the employee under section 22 or section 35 of the Health Protection and Promotion Act
• an email from a pharmacy or from a public health department indicating the employee’s appointment date and time to receive a COVID‑19 vaccination

Employers can only require the evidence at a time that is reasonable in the circumstances. What is considered reasonable in the circumstances will depend on all of the facts of the situation.”

Hope this helps!