Ontario and B.C. do not provide explicit credits for US estate tax
Since US federal and state estate taxes are inheritance rather than income taxes, they are eligible for a foreign tax credit only because of Art. XXIX B(6) of the Canada-US Treaty. Although, the majority of provinces have enacted legislation that aligns the federal and provincial foreign tax credits for US estate taxes, Ontario and B.C. have not done this - see 2010-0379381E5.
Another gap in the provincial tax credit system can arise in calculating the non-business-income tax credits where a Canadian tax treaty provides for tax sparing with a foreign country (such as Bangladesh, India. Brazil, Jamaica, Pakistan, and Nigeria). For example, 2016-0632711I7 indicates that Ontario taxpayers are not entitled to a provincial foreign tax credit on amounts spared under the Canada-Brazil tax treaty. This issue is more likely to arise with respect to non-business-income tax since the provinces do not have business-income tax credits for corporations.
Neal Armstrong. Summary of Kailey McLeod and Nadia Pulla, “Misalignment of Federal and Provincial Tax Credits,” Canadian Tax Focus, Vol. 9, No. 4, November 2019, p.8 under s. 126(7) – non-business-income tax.