If Pochettino is smart he just stays at Tottenham. He has one of the most talented strikers in the world, who's been literally carrying the team with 20+ league goals a season four years in a row (compare that to our forwards). He's got great talents like Eriksen and Alli in midfield, and better defenders than we've ever had for four years straight now. He wins nothing with them, but gets massive credit none the less to a point where some people act like he's a bona fide top manager.
If he just stays at Tottenham until the end of the season or even longer, so many big clubs will eventually come for him, like for example Bayern, Real Madrid, maybe PSG or even Barca one day. All those jobs are easier than the current/future United job, and if he'd take the United job and not be an unequivocal success within a year he can say goodbye to all the goodwill he's created so far. Or in short: it makes no sense at all for him to come to United.