The last I heard is that Pochettino might leave PSG, in which case PSG want Zidane to take his place. But Zidane himself wants to lead the French national team. It's hard to predict how the puzzle will play out, but the likelihood of Zidane ending up at United is very slim. I think United's ability to sign a great manager will depend a lot on where they finish. If it is top 4, then it will be a plus.
Didier Deschamp has done an excellent job with the France national team since taking over in 2012, and he will almost certainly lead the team to the next World Cup in Qatar. The chances of Zidane becoming the national team coach are slim unless Deschamp decides to resign, which is unlikely.
Poch's position at PSG will become available in the summer, and Zidane is the club top target right now.