The NAFTA has not changed the definition of expropriation in Canadian law. Canadian law already contained the concept of direct expropriation, as in this case, or of indirect expropriation, which involves other kinds of measures that result in you losing your investment. That has not changed with the NAFTA.
Also, people may, for indirect reasons such as an environmental regulation or some other regulation, challenge government measures either under the NAFTA or before the country's courts. However, if they do so under the NAFTA, they will not be successful. I have not seen any situation where government regulations intended to protect the safety of individuals or of the environment have been restricted.