The Bonus Taxation Method
Employers often make various payments to existing employees that fall outside of the regular pay period processing cycle. These payments could consist of bonuses, irregular commissions, banked overtime, etc. Additional payments such as these should be taxed using the bonus taxation method. 

The bonus taxation method is illustrated in Chapter 6 of the T4001 Employers' Guide - Payroll Deductions and Remittances. Employers may easily obtain a copy of the guide on the CRA’s website