Prior to becoming a resident of Canada for income tax purposes, a person will not be subject to Canadian tax on employment income earned in the US. Once a person has become, or is deemed to have become, a resident of Canada, he will be subject to Canadian federal and provincial taxation on his world income, including any employment income earned in the United States. To the extent taxes are paid in the U.S. on the same income, he may be able to reduce Canadian taxes through the foreign tax credit mechanism.

The main question which must be addressed is when one is considered to become a resident for the purposes of Canadian taxation. This question is complex and depends on the facts involved. Moreover, in the event both Canada and the United States consider a person to be a resident, the Canada-U.S. Tax Treaty has rules in order to settle this problem.

Disclaimer
The nature of this facility is to provide a general response to a general question. Under no circumstances should anyone act on this information without obtaining analysis and counsel from a qualified advisor with respect to the specific situation.

Phillip Nadler, CA
Richter Usher & Vineberg
http://www.richter.ca