Millar also won the sprint double for Aquinas College and the NZSS champs last year and said the pair would clash on Sunday in the 100m, as well as a likely showdown in the 400m.
Millar said it had only dawned on him in the last week that Harman was likely to be his biggest rival on the track in 2012.
"I'd say it's a pretty healthy and fun rivalry we have right now [both are coached by Todd Blythe] but I suppose when it comes down to it and we're lining up in the same race then there will be more intensity around that.
"Training together is enjoyable and probably what we need to get to the next level, because you find so many athletes are so secretive about what they do and don't want to share their knowledge with anyone."
Millar and Harman are both vying for a spot in the New Zealand 4 x 100m relay team for the London Olympics and head to the Brisbane Track Classic in two weeks to stake their claim.
Harman will line up in the 100m and relay at the Queensland State Athletics Centre, with Millar tackling the 200m, relay and possibly the 4 x 400m relay.
"They [selectors] will be looking at individual performances in the 100m and 200m before deciding on the team [six sprinters have been shortlisted], and then the team will try to post a qualifying time for London," Millar said.
"There's no absolutes but we've both made the initial cut from the long list."
Of the other confirmed entries for Sunday's meet, Cambridge's Camille Buscomb, a former top secondary schools athlete back from a shortened US track scholarship, will feature in the women's 3000m alongside Ariana Lord (Cambridge), the national junior secondary schools 1500m champion.
Tauranga's Amy Robinson, fresh from two junior titles at the national secondary schools champs, is set for a busy night, competing in the 100m, 200m, shot put, long jump, javelin and 100m hurdles, .
Te Aroha's Kerry White, the senior girls' 800m champion, and junior 3000m champ Jaob Priddey (Hamilton) will also be in action.
Sunday's Twilight meet gets underway at 2.30pm, with the children (10-14-year-olds) on the track until 4pm and the main meet running from 4.30pm-8pm. The 3000m at 7.30pm doubles as the Athletics Waikato-Bay of Plenty's championship.
The action returns to Tauranga Domain on Tuesday, January 3, when the New Zealand 10,000m champs are held.