How a proper accord agreement would have gone through "in real life"
Or as close to reality as the MCU was pretending to be. Instead we got the Hollywood treatment that affected the storyline as a whole - if the Accords had gone through the "realistic" route, Cap would have far less justification to do what he did.
- The Avengers will have found out (because apparently they have a superspy among them) on the political grapevine weeks or months in advance. Or at least have a strong suspicion. Nope, utter surprise despite 117 countries getting on board.
- There would have been input and negotiations involving dozens of politicians and policy-makers on something as vital as global security.
- If there was any respect whatsoever for the people who apparently "saved the freakin' world", they would be consulted before having a pile of documents thrown in their faces.
Expecting them to give up a major chunk of their operational independence UPFRONT without any previous negotiation is absolutely a slap in the face, not to mention risking EXACTLY what Cap did. These are not angry ex-military guys who can be restrained by handcuffs - we're talking flying hammer-wielding gods and angry green giants.
Essentially, it sounds like once they signed the Accords, only then will the UN decide how much freedom they allow the Avengers. That's negotiations for you.