Does the right to object to an expropriation or request an inquiry come from our Constitution? What exactly gives us this right, simply the Expropriation Act? If so, couldn´t the government change this at any time with an amendment to the Act?

The right to have an inquiry depends upon the applicable legislation. For example the British Columbia Expropriation Act provides a limited right to an inquiry. Similar inquiry procedures are found in other Expropriation Acts. There is no constitutional right to an inquiry so if a government decided to amend the legislation to repeal this right it has the power to do so.