Harrison and Davis won the men's and women's wildcard playoffs in Georgia to secure their entry to the first grand slam of the year under Tennis Australia's reciprocal arrangement with the USTA.
Harrison achieved promising results at the US Open this year, fighting through qualifying and upsetting world No.17 Ivan Ljubicic in the first round before losing to the 36th-ranked Sergey Stakhovsky in five sets.
Davis, who trains with the Chris Evert Academy in Florida, won all three of her playoff matches without dropping a set, taking her run of wins to 27 consecutive matches.
She recently won two ITF Futures events, the Junior Orange Bowl and the prestigious Eddie Herr Junior Championships.
Razzano, who reached a career-high ranking of No.16 in 2009, is currently ranked 114th due to an injury-interrupted 2010 season.
Twenty-one-year-old Paire, ranked world No.152, will make his Australian Open debut four months after qualifying for the US Open.