Yes, you can, but there are some key differences. It will taste different because cream cheese does not have the tanginess of sour cream. Also, because the cauliflower is roasted and devoid of moisture, sour cream is perfect because it introduces some moisture back to the mash. If you use cream cheese, it will be really, really thick. You might need to add a little water or a splash of almond milk to slightly increase the moisture content.