Canadian citizen working in the US

Hi,

A friend of mine is a Canadian citizen working in the US on TN visa. A portion of the year is considered a non-resident for tax purposes and paying higher taxes than residents. My question is, will be a tax refund for this portion of the year with non-resident status if he stays the entire year and then be considered a resident for tax purposes?

Another question is, should he pay taxes to Canada for the US income if he stays in the US for the entire year?

Thanks

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