It is important to remember that the provinces don't count on Ottawa for
their power. Their power is specifically mentioned in the constitution and
hence they have sovereignty over the areas given to them and the federal
government can't do anything to change what the provinces do in these
areas. That is what defines a federal state, that the federated units have
sovereign power of their own that the federal government can't act in, not the
form of representation the federal government uses.

So as you say the UK where the UK parliament has devolved some of its power
to regional parliaments, but the regional parliaments can have that power
taken away by the UK parliament at any time. On the other hand, in Canada
for example, what the provinces have exclusive jurisdiction over is outlined in
section 92 of the constitution. So for example if Alberta wanted to do away
with medicare, it could. All the federal government could do about it is stop
sending money for health care as non-marine hospitals are exclusively a
provincial power.