As you no doubt know the last payment for source deductions taken in 2016 is due on January 15, 2017. Seems simple but there are a couple of things that you should do before you send in that last payment.
Do you have any employees that have taxable benefits? These are items like standby charges on company owned vehicles and insurance paid for by the employer. The inclusion of these benefits on a T4 for an employee could mean that they owe Canada Pension Plan (CPP) and you as an employer have to match that payment. If you pay source deductions after January 15, 2017 for the 2016 year you will pay interest and possibly a penalty. So, do your 2016 T4’s with all the taxable benefits before January 15th and be sure that you do not owe any more money.