Canadians pay 50% of their income tax rate on capital gains income. So if I pay 43% income tax, I pay 21.5% on capital gains.
Americans pay 15% on capital gains (or 0% on capital gains for the lowest two income tax brackets)
Technically it's that 50% of our capital gain is subject to taxation but the math works out the same so who cares?

Still, if that 39% number Stienman was tossing around is correct... that's a pretty huge jump from 15%.