Netherlands/Canada, sometimes abbreviated NedCan, NetCan or CanNeth is a pairing involving the characters of Canada and the Netherlands.
Despite never interacting in the manga or anime, the countries are known to have one of the closest international relationships in the world, stemming mainly from Canada's role in the Liberation of the Netherlands during World War II. Canadian forces moved through the Netherlands, retaking cities from German forces as they went. The Canadian air force delivered food into the still-blockaded provinces. Once the last Germans had surrendered, the Canadians moved in and began rapidly distributing much-needed food and supplies. As a "thank you", the Dutch people sent thousands of tulips, the national flower of the Netherlands, to Ottawa. The gifting developed into a tradition: the royal family has sent ten thousand tulips to Canada each year since the liberation.
Many fics with this pairing involve giving and receiving tulips. Another common topic is shared drug usage. This is most likely due to the liberal policy that the Dutch government takes towards recreational pot, as well as the perception of Canadians as relatively liberal people, and thus apparently more inclined to drug use than others.