(Unsure if this belongs on Law or Politics SE, it might be better suited for Law)
Apropos of Prime Minister Justin Trudeau invoking the Emergencies Act against the Freedom Convoy in Canada earlier this year, something's been bugging me.
It seems to be the case that the Prime Minister is able to invoke the Emergencies Act, for the most part, whenever he wants, without checks and balances before the fact (there are checks and balances after the fact, within 7 days, but not before). It also seems like, even if the Act is revoked and/or judged to be used improperly, there are still lifetime repercussions to those against whom the act was used.
Given that the Act can be invoked without any check beforehand, what, legally, is stopping a given Prime Minister from invoking the Act against the opposition parties, "just because"? Concretely, this would take the form of the Act being invoked, assets/bank accounts/etc of opposition politicians and supporters being frozen/seized, then within 7 days before the oversight would be handled the Act would be repealed, an "ok emergency's over!" statement would be issued, and those people whose assets were frozen would have lifetime flags on all their financial transactions. Certainly, if the Act was invoked, as in this case, even if it was repealed, there would be a followup confidence vote in Parliament, and the government might fall, but is that the only check against this sort of action, or are there others?
EDIT: In case the question is unclear, here is an excellent rephrasing of the question from the comments:
It seems pretty clear that OP is asking what the specific legal provisions and procedures one would rely on to remedy misuse of this act, or to prevent misuse from being enacted in the first place. I.e. if the government simply declared that inconvenient opposition MPs were causing a "public order emergency" and took some action against them, who has the power to stop them and declare "no, that's not what 'public order emergency' means".
(credit to /u/Ben)