Hello and thank you for using Just Answer,The US?Canadian tax treaty covers you as long as your worldwide holdings are not more than $5mil. A Canadian citizen whose worldwide estate is less than $5 million is not subject to US estate tax, no matter how much property has a US situs. See Article XXIXB2 of US-Canada Treaty. Even if a Canadian citizen’s worldwide wealth exceeds $5 million, there is no US estate tax if US situs property is less than $60,000. Code Section 2102(b)If the above fits your estate situation then your estate would not pay tax when you are deceased.Your daughter would need to report any bequeath that she receives if the amount is over $100,000 (in value or cash). She would not be taxed but she would need to report using Form 3520. This would only be on her portion as she is a US citizen. Your son would not have a reporting requirement to the US as he is not a US person.
The share certificate would be considered a non-tangible asset by the IRS?
The U.S. Internal Revenue Code s. 2104 states that "shares of stock owned and held by a nonresident not a citizen of the United States shall be deemed property within the United States only if issued by a domestic corporation". If the corp is a US corporation then the share certificate would be included in your US estate.