On Xbox in TSW or TSW2 there isn't a way of switching cabs without getting up and walking to the other cab. I'm not totally sure if you can do it in classic controls with the internal camera sub menu.
There isn't a way to quickly switch cabs in TSW/TSW2 using the controller. There is, however, keys assigned to cab switching if you use a keyboard.
Left and right directional arrows to switch cabs with keyboard. Then you need to use classic controller scheme to interact with cabs, with the new one you can't.
It's Ctrl + to physically move to the next cab. Very good way to save time on Peninsula Corridor for turning the marker lights on at the other end.