An employee derives a benefit from free parking unless the employee must use the space “regularly” to perform his or her employment duties (ie for business purposes). Parking “to facilitate working irregular or extended hours is [not] parking for business purposes.” CRA technical interpretation dated January 24, 2018 (2016-0645911E5), translated and summarized at taxinterpretations.com here.
Update July 21, 2018 For a discussion of this technical interpretation, see Georgina Tollstam, “After-Hours Parking Spot Is Taxable Benefit” 26:6 Canadian Tax Highlights (June 2018). She points out that the CRA position is contrary to the Tax Court decision in Chow v R, 2001 DTC 164 (informal procedure).
