As per CRA - You can distribute T4, T4A, T5 or T4FHSA slips by email. If you distribute by email, you must receive consent from employees or recipients, in writing or in electronic format, before sending the slips by email.Dec 13, 2023

Once receiving consent then you need to print the employee's copy of the T4 to a pdf file. One common printer is called 'CutePDF'. Then you can email the pdf T4 to the employee.