Doesn't the income tax treaty help in that case? Quoting from https://www.irs.gov/pub/irs-trty/canada.pdf: "Subject to the provisions of Articles XVIII (Pensions and Annuities) and XIX (Government Service), salaries, wages and other similar remuneration derived by a resident of a Contracting State in respect of an employment shall be taxable only in that State unless the employment is exercised in the other Contracting State. If the employment is so exercised, such remuneration as is derived there from may be taxed in that other State."
I'm aware of the foreign income exclusion you're refering to, but wouldn't the tax treaty have a higher priority?