"We should be reasonably strong on the bike and run but, I think, the paddling will be a bit of an unknown for us."
Olly, 24, is a world-class triathlete who competes in Xterra (off-road triathlon) events around the world. Sam, 23, is a top mountain biker and is currently targeting enduro racing.
While the course looks gruelling, Olly said he was looking forward to having a crack at it.
"It just looks like an amazing course really and the competition is world-class. That was a big drawcard for me - the course and the people that are racing."
He said they felt they had a chance at making the podium but the kayaking would be unfamiliar territory.
"I guess both of us are pretty competitive and I like to think our biking and running will put us in a pretty good spot to compete for a podium place.
"But a lot will come down to the conditions and how the kayaking goes for us. I'm hoping it is windy and we get plenty of help with the wind blowing behind us [on the river]."
Race director Aaron Carter said he thought the 2016 version was shaping to be even bigger and better than their first event in 2014. He said a field of about 50 teams had entered this year.
"We are on the verge of delivering the second instalment of Red Bull Defiance and are thrilled with the increased number of teams and quality of the field," Carter said.
"We have got a number of highly skilled staff and volunteers that are putting in some big hours to ensure we put on a top-level event."
The course is designed by New Zealand Coast to Coast champion Braden Currie.
Currie, who won the inaugural event with Dougal Allan in 2014 but is not racing this year, said there was some stiff competition entered: "Within the men's field there are two young guys, Alex Hunt from Tasmania and Daniel Jones from Whakatane, who are both really good and I've never seen them race together before.
"There's also Jarad Kohlar and his partner James Pretto, and local guys Richard Anderson and Bob McLachlan."
The successful entrants this weekend will take home $10,000 for first place, $3500 for second place, and $2500 for third place in the elite men's, elite women's and elite mixed categories.