A country like France is a unitary state. While there are departments/"provinces" that have powers, those departments only get their powers from the centralized authority. If a constitutional amendment were to occur, the departments have no authority to override the central-authority's approval.

The United Kingdom is also a unitary state. While Scotland, Wales, and Northern Ireland have powers, these powers can be given and taken away at any time by Parliament in London.

France is a republic while the UK is officially a monarchy.

One aspect of federalism is that the units/provinces/states usually have authority to change or oppose changes to a constitution. The central state exists because the sub-units have formed together and agreed to share power. The central state usually has no power to change the constitution without the consent of the sub-units.

Another difference among unitary, federal, and confederal states is representation in the central institution(s). Usually (but not perfectly), democratic unitary states have representation by population. Federal states have a balance between representation by population and by sub-states. This is true in the US with the House of Representative and the Senate. Confederal states or institutions usually have representation by territorial units. For example in the UN, the United States and Luxembourg have one vote each in the General Assembly even though the United States has a much greater population.

In Canada, we essentially have a federal state in which the central institution is essentially run like a unitary state. The House of Commons is supposed to represent the people by population. The Senate which in theory is supposed to represent the regions is un-elected and usually doesn't challenge the authority of the House of Commons. While Canadians like to call Canada a confederation, I think Canada is more federal with a unitary style central institution. That's just my opinion.