When you withdraw funds from an RRSP, your financial institution withholds the tax. The rates depend on your residency and the amount you withdraw. For residents of Canada, the rates are:
For funds held in the province of Quebec there will also be provincial tax withheld. For more information on Quebec withholding, contact your financial institution or Revenu Québec.
The tax that was withheld may not always be enough to account for the tax you owe at your tax bracket. You may have to pay more tax on the withdrawal when you include the withdrawal on your tax return for that year.
For non-residents of Canada, withholding is 25% unless reduced by a treaty. See IC76-12R, Applicable rate of part XIII tax on amounts paid or credited to persons in countries with which Canada has a tax convention.