For rental property, you can claim CCA against your rental income. When you sell the rental property, you will have to do a CCA recapture.
For example, in 2012 you bought a rental property for $300K. You
can claim up to 1/2 of 4% of $300K = $6,000 CCA, providing your rental income is at least this amount.
Assuming you sell the property this year at $320K. You have to pay tax on the $6K recapture CCA you claimed in 2012 and the 1/2 of $20K capital gain.