HK. Yeah, if you asked me out of the blue what 棉花糖 is I would've said cotton candy first but I also had a vague memory of calling marshmallow that too. I had to confirm it with Wikipedia lol.
No it’s the same. Then again I can’t recall seeing any marshmallow on the shelves when I visit home. I don’t think it’s a common snack in Taiwan but I could be wrong!