I can't say for sure but you might check this out: http://woodworking.stackexchange.com/questions/2068/can-i-apply-water-based-polyurethane-over-an-oil-based-stain
I don't recommend it bc it's water based poly. It made my beautiful Kona cabinets streaky like I had poured milk on it & let it dry. I called customer service & was told I "over worked" it by going back and forth with my brush more than twice. So I tried it again using just 2 strokes. Cabinet came out less hazy & streaky, but still is terrible looking. Use oil based poly for oil based stains!
I use this product over paint as a sealer. It may darken the wood slightly if it is unfinished (raw) wood.
Yes. As others have said it goes on white and dries clear. I can send a picture I a finished product if you would like.