https://www.taxtips.ca/personaltax/investing/taxtreatment/are-your-investment-gains-and-losses-capital-or-income.htm
Are Your Investment Gains and Losses Capital or Income?
For most taxpayers, their gains and losses from the sale of securities are treated as capital gains and losses. This means 50% of the gains are taxed instead of 100%. A capital loss can only be used to reduce or eliminate capital gains.
Frequent Trades Can Be a Problem!
For some taxpayers, such as day traders, the gains and losses are determined to be business income, not capital. This means 100% of the gain is taxed, and 100% of a loss is deductible. The business loss is deductible from other income, and if the loss exceeds other income it becomes a non-capital loss. Both the conduct and intentions of the taxpayer are examined to determine whether to treat the securities transactions as income or capital. The combination of a number of the following factors may cause the gains or losses to be treated as income (100% taxable), not capital (50% taxable):
frequent transactions, extensive buying and selling of securities
short periods of ownership
some knowledge of or experience in the securities markets
security transactions form a part of the taxpayer's ordinary business
a substantial portion of the taxpayer's time is spent studying markets and investigating potential securities purchases
security purchases are financed primarily with margin or debt
the taxpayer has advertised or otherwise made it known that he is willing to purchase securities
securities purchased are speculative in nature or do not pay dividends
Short Selling
A person is "short" a security when they sell shares they do not own, by borrowing them from their brokerage company. This is called making a "short sale", or "selling short". This is normally done when the person believes that the price of the security is going to fall, so that they can cover the sale by buying back the stock later at a lower price. See also "long".
The gain or loss on the short sale of shares is considered to be an income gain or loss, unless an election has been made under s. 39(4) to treat them as capital transactions, if they are Canadian securities. In Federal Court of Appeal Rezek v. Canada (2005 FCA 227), it is stated that any broker's fees, rental fees and compensatory dividends paid by the short seller between the short sale and the close out will reduce the profit or increase the loss.
Some Capital and Some Income Transactions
It is possible that a taxpayer may have some securities transactions which are capital transactions, and in the same year have other securities transactions which are income transactions. For example, a day trader could have two investment accounts, one for day trading, and one for investments which are not frequently traded, and are held as long term investments.
For RRSPs and RRIFs, s. 146(4)(b) and 146.3(3)(e) specifically exclude from business income any business income from qualified investments, or from the disposition of qualified investments. This means that someone could engage in day-trading in their RRSP or RRIF without being taxable on the business income until the income is withdrawn. This exclusion does not apply to other registered accounts, such as Tax-Free Savings Accounts. See links below.
Excellent article on whether stock transactions are capital or income: Vern Krishna: Stock Traders Beware of Tax Traps: The Taxman Cometh
This topic is discussed in the April 2021 Life in the Tax Lane video from Video Tax News.
Election to Treat Transactions in Canadian Securities as Capital Transactions
A taxpayer can elect under s. 39(4) of the Income Tax Act to have their transactions in Canadian securities to be treated as capital transactions. The election is made by filing Form T123 Election on Disposition of Canadian Securities, and applies for Quebec taxation purposes also (as per Quebec Taxation Act s. 250.1).