Legally, the company is only required to grant the statutory holiday to employees who work in British Columbia. Employees in Alberta and Ontario are not entitled to have September 30 off as a statutory holiday, as it is not legislated in those provinces.
That being said, the company has the discretion to extend the statutory holiday to all employees, regardless of their location. It can be a goodwill gesture to offer the same benefit to employees across all offices, even if they are not legally required to do so.