By being a US-based company, they are also subject to US law.
If you believe you have a general solution to the problem of incompatible edge cases in international financial regulation, there are many, many companies who would be willing to make you a very rich person in exchange for that information.
The Square Canada corporation may still be directly prosecuted for violating the Foreign Extraterritorial Measures Act. It is designed to prevent the United States from interfering with Canadian business.
That Square Canada has a parent corporation is immaterial. Seize assets from the Canadian company to pay the $1.5 million fine for violating the act.
If this is unacceptable, then Square Canada is no longer a legitimate business and Square can't have a legally operating subsidiary in Canada.
I don’t have a solution for the general case. I do think I have a solution for the specific case: Mustelier would have to get a Canadian lawyer and sue for damages plus lawyer and court fees. Square Canada would settle for this amount and ask her to sign an NDA and offer extra for her to sign the NDA. Square Canada would write-off the settlement as a loss. Square Canada would forfeit the amount frozen by JP Morgan Chase.
Yes, this solution is probably still not good enough. Maybe Square Canada’s US parent would still have to pay a fine.
I understand the what US law will be broken if JP Morgan Chase releases the funds in that a U.S. entity would be party to a transaction involving Cuban goods. However, right now, said U.S. entity is effectively party to a theft involving Cuban goods and Canadian funds.
If you believe you have a general solution to the problem of incompatible edge cases in international financial regulation, there are many, many companies who would be willing to make you a very rich person in exchange for that information.