Fair though it’s more than the plateau. Mile end, rosemont, little Italy, mcgill ghetto, outremont are all like this. And then while other areas don’t have quite as many criss crossing streets, they are still very walkable and mixed. (Cote des neiges, st henri, ndg, westmount etc)
I’m sure I’m forgetting some neighbourhoods too. Mostly describing those I personally walked around a lot. The mountain gets a way a bit for those in the second list, whereas the areas around the plateau are a square grid of similar neighbourhoods in all directions.
But I agree, from the North American cities I visited, Montreal has the nicest, livable higher-density housing areas.