You mean flyover? It seems to be on by default wherever it's available now but the view stays overhead until you use two fingers to change the angle. Once you've changed the angle a "2d" button appears to change back to overhead (but still 3D)
The 3D button is gone indeed and the maps themselves look like a 2.5D in the driving mode now, hope they can tilt it better before the final release is out.
The 3D button was remove and to get into 3D mode you two finger drag up on the map. (See screenshots. Screenshot 1: in 2D mode. Screenshot 2: in 3D mode with button to get back into 2D (but two finger drag down also works to get back into 2D))