For sure a somewhat bigger engine to make the car appear to work better ( quieter anyway) with an automatic transmission and do 0-60 faster at the expense of 45-70. EU drivers can buy diesels with lots of low down torque to drive a slushbox, we will not be given that option, we'll just get the biggest engine that fits... and then people will complain that it is underpowered ( like the Saturn Astra).
Brakes with better low speed "bite" that will fade if used too hard at higher speeds.
Cup holders. Softer and flatter seats. (North) Americans are bigger than Europeans and they can't make a wider body without making it a different car altogether so the seats have to be made wider.
I'd bet that a well optioned Vectra straight off the German dealer's lot with just the emissions changed for here would be a pretty nice car but might end up being in the wrong price bracket here. I am sure the NA one will be decontented in various ways. No HIDs will mean no headlight washers and no self leveling. Red rear indicators and no rear fog light mean less wiring in the car and so on