Haris should have been tried out as opener ages back, but I think it's unrealistic to expect him to open, don't think he's ever done. Babar opening is a bit more realistic as he does it in domestic, and does it in T20s, but even that don't think management will want to risk it before the WC again needed to be done a few series ago.
Abid coming in for Imam is probably the way, hopefully he'll have a similar impact to what Fakhar had at the CT, it's clear Abid's talented, has the shots, right handed for right-left combo and performing in domestic. Think it's a good risk to take.
I think's it more down to Haris, Hafeez and Asif for the remaining slots. You could make a case for any of the three all have their pros and cons. Pretty sure Haris is the more reliable bat, but lacks ability to accelerate more than the other two. It's extremely irritating Haris hasn't played many ODIs since he came back from injury, was thoughtless by the Coach, giving chances to Imam but carrying Haris on in the squad. I get they are similar cricketers to an extent so hard to fit in all at once, but really we should have made sure Haris wasn't ODI material or not. Instead we're carrying him in the squad, as we still don't know.
I'd go with Haris just because of his talent and reliable scoring. Hafeez or Asif is the tough one. Hafeez is showing increasing struggles to play pace probably due to his age, and think would be eaten alive opening or at 3 now. He was never great at it, but held his own there in the past and of course added more to the team batting +bowling, and there were less good batsmen in the team in the past for him to compete with. Asif has better hitting abilities but there are doubts on his consistency due to his domestic record and I do wonder if he hold up against spin. Hafeez's experience will help too in terms of guiding his team home, and maximising the runs against the weaker/spin bowlers. People then again overrate Hafeez's form, he too has been in and out of the team lately, you don't know whether he's in rich form or not.
I was leaning to Asif, but honestly it's a coin flip, I don't really know who I'd pick between these two, it's a really tough decision.