Effective September 5, 2017 the settlement date for the purchase or sale of investments such as stocks, and bonds, will now be two business days after the trade date instead of three. For call options and put options, it is one business day after the trade date. The purchaser does not own the investment until the settlement date – which is important to note if the trade occurs around year end, as the gain or loss is recorded in the tax year of the settlement date.
Thus, the last date to trade stocks in Canada for the 2017 year is Wednesday, December 27 (keep in mind the statutory holidays on December 25 and 26). Anything purchased or sold after December 27 will be settled in 2018.
Source: http://www.taxtips.ca/personaltax/investing/taxtreatment/tradeandsettlement.htm#settlement-date-t+2, accessed November 23, 2017