Canada Revenue Agency rules state that the settlement date, not the trade date, is the determinant of when you have disposed of a security.
Hence, if you wish to liquidate stocks on the public exchanges and have these transactions count for the 2018 tax year, you have until the close of trading on December 27, 2018 to do so for the trade to settle on December 31, 2018.
I would expect given that Q4-2018 has been one of the worst performing in quite some memory, that this would be a consideration for many investors to have the CRA share their losses in 4 months (when filing for taxes) than 16 months later.
[…] PS. Canadian investors have until the end of the day on the 27th to sell for the tax loss, as noted by Sacha at the excellent Divestor blog. […]