It will be a civil union, as marriage is between a man and a woman.

Nope, at no time in it's history have NZs marriage laws ever been based on or influenced by Christianities interpretation of marriage. So no, whatever meaningless rituals you decided to perform aside it all boils down to a legal contract and legal state recognition and always has, so my marriage will be just as real as yours.

Considering the fact that the concept of marriage existed in every culture and religion for thousands of years before your particular religion was ever even thought up it always seemed strange that this was the hill you decided to die on. Up until the late 19th century "traditional Christian marriage" was child marriage, inter family arrangements and women being treated as slaves to their husbands.

But that's the hill you chose, so so be it.