I am a Canadian citizen living and working in the U.S. for a U.S. employer on a visa. Do I need to file both a U.S. tax return and a Canadian tax return?

You must comply with both U.S. and Canadian filing requirements, if any. In the United States, you generally are required to file a return if you have income from the performance of personal services within the United States. However, under certain circumstances, that income may be exempt from payment of U.S. tax pursuant to the U.S.-Canada income tax treaty. You need to determine what type of visa you have, and how that impacts your residency status in the United States. If, based on the tax code and your visa status you are treated as a U.S. resident, then your entitlement to treaty benefits will be impacted. You must contact the Canadian government to determine whether you must file a Candian tax return and pay Canadian taxes.