In the modern world countries work together on basis of mutual interests. Pakistan and Bangladesh will work on commonalities but it doesnt contribute much beyond it till the roots are fixed.
Best way to fix things is (In the short term) send cultural people like Fawad Khan, Nusrat Fateh Ali Khan and other Pakistani celebrities/artistes to Bangladesh, along with the Coke Studio performers, to captivate tastes of educated and sophisticated young people. I promise you they will be performing in packed arenas (stadiums) wherever they go in Bangladesh.
Last time Fawad was here five years ago, twenty something university women were ready to go home with him. The screaming was unbearable. Gotta use these as cultural ammo.
ARY, HUM, GEO channels are already extremely popular in Bangladesh as are Urdu soaps which these channels broadcast. Bengali subtitling will make them more popular, though Bangladeshi aunties know most Hindi words in any case.
Send in all your MBBS students (and students of other programs) to Bangladesh, and provide SAFTA arranged scholarships if necessary. Most Pakistani students find cultural differences to be minimal, if any. We must use person-to-person contacts among young people to fix the problems for the next generation.
Then in the medium term fix the trade gap relationship (Pakistani imports in lieu of Indian imports to Bangladesh) which will benefit Pakistan as well. Arrange Pakistani trade fairs in Dhaka to ensure Pakistani handicrafts and small industry products are demonstrated like metalware, copperware, sialkot sport products and cutleries.
The rest will take care of itself.
I know - a bit trite and somewhat crass game plan, but I don't believe in complicated game plans, which don't work.
But
@Atlas Bhai is right, assuming rigid unhealthy attitudes on either sides will not help matters. Distrust was created in 1971 and Sanghis made 100% hay out of it and this is their main weapon in Bangladesh. That distrust for Pakistan created by Sanghi propaganda will take actual time and actual EFFORT to overcome.
We have educated and sane people on both sides, all we need is political will, determination and an appetite on both sides to eat a bit of unsavory humble pie, but only as a temporary thing. Considering the long term benefit, it must be undertaken.