I’ve never made sunflower seed milk, only nut milk but here’s one…

1 C sunflower seeds (soak about 4 hours or over night for best results)
2 to 2 ½ C water (depends on how thick you like it)
1 T honey (optional)
1 tsp cinnamon (optional)
Blend then strain through cheesecloth or a fine metal strainer

You can use the same recipe for almond or walnut milk just increase water to 2 ½ to 3 C. 
If you’re just using it to cook with I’d leave out the optional items but if you’re drinking it straight it’s probably better with them or you may have to adjust to taste.