The pair train together on the Gold Coast at the Northcliffe club.
"I spend most of my days with Cory and he's my best training partner so I know exactly what he's capable of," Beattie said. "He's been doing some hard yards in training and he's pretty fit so I'm looking forward to racing him over the short-course."
Also in contention is Whangamata's Bjorn Battaerd, while Katie Wilson (Mount) and Danielle McKenzie (Mairangi Bay) look set to continue their duel after McKenzie won the 25km women's Monster last week by just three seconds.
It's been 18 years since Omanu clubbie Ian Porteous died, aged 44, the day before the club's annual long-distance ironman race.
It prompted his mate Denny Enright to establish a memorial race for the Mount College teacher, conservationist, family man and marathon runner.
Other previous winners include Aaron Jarman, Cory Hutchings, Mark Muir and Matt Sutton, who are all past New Zealand representatives.
Jarman (1995 and 1996), Sutton (2006 and 2009) and Munro are the the only double winners, although Beattie is keen to remedy that.
"The Ian Porteous Memorial is a special race ... Up until last year, I was pretty desperate to win it and it weighed on my mind a bit but now I'm really keen to defend it, not only for me but for the club. It would be great to keep it in-house."
The Omanu Classic is a fast-paced afternoon carnival with a heap of spot prizes on offer. It features a full range of board, ski and swim events.
Racing starts at 12.15pm, and a large number of late entries are usually received on the day.