Exclusive rights to the wedding have been granted to a women's magazine, but details are starting to leak out.
While gay marriage has not yet been legalised, it's understood the couple will join in a civil union and consider it a marriage.
Timaru band Coyotes are to play and the event will be held at the couple's shared business, Topp Lodge, in Staveley, northwest of Ashburton, which offers fully licensed functions for up to 80 people.
Topp, of Topp Twin fame with sister Jools, and Ms Luxton set up the accommodation so they can have bed-and-breakfast guests whom Topp can take on hunting and fishing trips, the New Zealand Woman's Weekly reported in 2010.
The couple are well liked in the area and have been seen holding hands across the table while out for dinner.
The Topp Twins' agent, Arani Cuthbert, said the rights to the ceremony had been sold to a women's magazine and she'd "been sworn to secrecy" so couldn't give details.
In an article in Woman's Day last year that announced their engagement, the couple revealed their marriage ceremony will be a "big, old-fashioned country-style hoedown", with Ms Luxton wearing a "Dolly Parton-style" dress.
They told the magazine how they coped with Ms Luxton's growing realisation that she loved Topp.
Topp proposed the pre-school teacher during a Bali holiday trip last year. They met at the Methven A&P show in 2005 at which Ms Luxton was supporting one of her sons, a singer then aged 11.
Cameron Luxton went on to become a support act for the Topp Twins at events such as Australia's Tamworth Country Music Festival.
On Wednesday, a parliamentary select committee recommended that a bill to legalise same-sex marriage be passed into law.
The legislation's second reading will be held on March 13.
It passed its first reading by 80 votes to 40.
- Amelia Wade of the New Zealand Herald
