Assuming you want to process array of array sequentially in row-major approach, this should work:
int[][] arr = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };
IntStream stream = Arrays.stream(arr).flatMapToInt(x -> Arrays.stream(x));
First it invokes the Arrays.stream(T[]) method, where T is inferred as int[], to get a Stream<int[]>, and then Stream#flatMapToInt() method maps each int[] element to an IntStream using Arrays.stream(int[]) method.