Drain cashews and sunflower seeds and add to blender or food processor along with water (or dairy-free milk), lemon juice, vinegar, nutritional yeast, salt, and garlic. Blend, stopping to scrape down sides of container as needed, until mixture is as smooth as possible. If very thick, add additional water or dairy-free milk, 1 Tbsp at a time, to arrive at a thick, spreadable consistency.