I'm not in HR or a lawyer but I found:
https://www.alberta.ca/alberta-general-holidays Says:
Optional general holidays
Employers can choose to recognize additional days as holidays. If an employer recognizes an additional holiday, all employment standards rules related to holiday pay apply to these additional holidays.
Employees may ask their employer if they recognize any additional holidays.
Optional holidays can be any day an employer chooses to recognize. Some commonly recognized optional holidays in Alberta include: Heritage Day is listed here
So if all employment standards rules related to holiday pay apply, then this
https://open.alberta.ca/dataset/0608...idays-2023.pdf says:
Not working on a general holiday
If an eligible employee does not work on a general holiday that is a regular day of work, the employee is entitled to their
average daily wage