Sharjeel needs to play next game under any circumstances. I would drop Azhar and bring him in. I know that two lefties opening would not be a wise move thus, I think Sarfraz should open next match. Agreed, this is not a time to experiment with the series mid-way but Sarfraz has previously been entrusted with this role in ODI's and come good and even has a ton opening in Aus.
But there's more to it than just this. Next match is Boxing Day test. The stadium will be packed. I don't think Sami Aslam and Azhar Ali have the confidence required to come good opening in front of a crowd of 50K people. Sharjeel and especially Sarfraz have the quality to take pressure. I feel like they're players who come good in pressure games. An example of this would be the Asia Cup final 2012 where Sarfraz played a vital knock when Pakistan was struggling even though he was half the player then that he is now.
Another important aspect of this would be that we've seen our top order is taking too much pressure, blocking too much and not playing the ball but the reputation of the bowler. The lower order and Sarfraz did good because they didn't have to take any pressure. They weren't blocking everything and playing the ball to its merit. Even Asad Shafiq did not block unnecessarily and that is why he played good. Sarfraz and Sharjeel are exactly those players. They play quick and even if they get a 50-60 run opening stand, it would be more than enough.
Not to forget, Sharjeel has already shown ability to play express pace first up and play it good vs England, so he may negate Starc. He also thrives on playing fast bowlers and that is what our batsmen have seemed to have an issue with. Sarfraz is basically the same, he is more comfortable IMO playing fast bowlers than most guys in the, except I don't know think he's as good AS Sharjeel at express fast bowling.
Azhar Ali can sit this one out like Yasir Shah did at Hamilton.