First thing is to answer what culture in EU2 means. Is it an ethnic term or does it represent a political affiliation/loyalty towards particular state.
It culture is an ethnic term, then city of Danzig/Gdansk should be Dutch or Flemish. Most of the city's wealthiest burghers came from Netherlands, bringing their businesses with them. Also the city's architecture resembles that of the Low Countries. The city was in fact not germanized before 19th century. It was rather a multicultural melting pot with Poles, Germans, Dutch, Scots, Jews and God-knows-what-else.
However, we should also remember that the rural areas around Gdansk/Danzig were predominary Polish and the province itself was predominary Polish.
If we consider culture as affiliation/loyalty, then the city should be Polish. It voluntarily submitted itself into Polish crown and many times proved its loyalty (for example in 1655, 1733, 1792) by fighting the enemies of the Polish crown.