Tax Planning for You and Your Family 2019 by KPMG. p 196.
12.2.3 Allowances and advances for automobile expenses
If you receive a reasonable allowance for automobile expenses, the allowance will not be included in your income if it is based solely on the number of kilometres driven in the performance of your employment duties. If it is a flat
amount not calculated in terms of your employment-related driving, it will be taxable (though you may be able to claim offsetting automobile expenses—see 12.3.1). The CRA will agree to consider a flat periodic amount to be an accountable advance (rather than a taxable allowance) if you and your employer agree at the beginning of the year that you will receive a reasonable stated amount for each employment-related kilometre driven and you and your employer settle up at the end of the year regarding the difference between your actual business-related kilometres and the stated amount.