The employee has a residence in one province but goes to work in another - which province do I use for the 'Province of Employment'?

The employee's 'Province of Employment' is the province where the employee is required to show up for work, regardless of the employee's province of residence. Payroll deductions are always based on the province of employment, even though the employee's income tax return for the year will calculate the final income tax liability based on their province of residence as at December 31.