Not that simple since our canadian tax system is complicating everything. Very simply summarized it goes as follows:
50% of your capital gain of the year is added to your taxable income, therefore taxed at your marginal rate.
50% of your capital losses can be deducted from your capital gains going back 3 years or forward 7 years.
Therefore to be able to account for capital losses, you must have had net gains within the last 3 years or keep them aside till you get some within the next 7 years.