The province is made up of several islands which is most likely why it was chosen as the name for the islands found in the south pacific.

It is thought to mean ‘sea land’, though another opinion thinks it might be a shortened form of Suevan land, named for the German tribe called Suevii.

If Sea land, it is quite an appropriate name because that is exactly what New Zealand is. Even the maori names for the north and south island have sea themes with the fish of Maui and the great canoe.

The links show maps of The Netherlands and Zeeland.

BTW, Holland is a region within The Netherlands, but because it includes most of the coast facing Britain, the British call it Holland (there was also a Kingdom of Holland at one point, but The Netherlands is larger than that was).

Zealand was a maritime province of the Netherlands.