The latter is far more realistic of a scenario. Though Brees and the Saints aren't done negotiating yet, he's been franchise tagged, he's not going anywhere. Even for a player of Brees' skills, the price is too high to pay for any team to trade for him.
Manning on the other hand is a free agent and Kansas City has got to be considered one of the more legitimate possibilities for a landing spot for him. I don't think he's a long term solution for anyone being 36 and coming off of neck surgery, but the truth is, every QB is one hit away from oblivion. It's the nature of a violent sport like football no matter how much Emperor Goodell tries to obfuscate that with suspensions. If Peyton can still throw the ball, I could see a team look at him as a short-term possibility. It'll sell tickets, that's for sure. That said, neither of my teams (Jets, Bucs) need to get involved in the chase.