You want to evoke a sense of difference to each major metro area, while keeping in mind that most forces are trying to force them into the same mold
One thing Boswash will have going for it is American History. Everywhere you go, there will be historical markers for Who Slept Here, old battlefields, meeting houses, where Important Documents were signed, on and on. Whole areas will be picked out in their own augmented reality layer, detailing salient historical sound.video bites. ("Follow the green trail - This AI reconstruction of Paul Revere's ride passes through..."). Some areas will be almost completely subsumed by nostalgic recreations of the past.
One major thing you could add to distinguish Boswash is that, unlike New Angeles, it has land area to grow - and it can even make new land. Look at changing some areas of the coast. Fill in Chesapeake Bay or have it covered by a floating industrial complex. Redirect major rivers into sculpted eco-canyon recreational areas. Add sculpted seawall/power stations to Long Island. One thing they can boast would be parks large enough to be called wilderness. Greenspace strips regularly break up the parade of buildings. Lots of things are underground - most infrastructure, poorer living quarters, etc.
Farm towers. You can easily feed a city the size of Boswash with towering farms that use the city waste to produce a truly massive amount of food. Emphasize almost every vertical surface has something growing on it, and most times that thing is meant to be harvested and eaten. Plants that don't do well in X urban condition (shade, dryness, whatever) are engineered TO do well. Bioreactors turn waste into printable organics indistinguishable from harvested animal protein.