I have questions about pension income from Canada, where tax is withheld in Canada. How do I enter this for US taxes?

You will enter as Income (see link below) You will then enter the tax paid to Canada as a Foreign Tax Credit or Deduction.  

The taxation of payments received from Canadian retirement programs that are similar to the U.S. Social Security system receive special tax treatment due to an income tax treaty between the United States and Canadian governments. The way this income is taxed depends on the recipient’s residence.

How do I enter my Canadian Pension Plan (CPP)

Where do I enter the foreign tax credit

Thanks for the response.  In this case the Pension in question is not CPP, but rather from a previous employer.  Do I use the same approach?

Yes, you would use the same approach to report pension income that comes from a previous employer.