Stack is expected to be fit for the start of the new campaign after undergoing surgery for a shoulder ligament injury that he sustained in March against Hamilton.
The Englishman began last term as first choice under then manager John Hughes but went on to make just seven appearances after also struggling with a persistent back problem that kept him sidelined for five months.
Calderwood handed Stack a one-year deal this summer, freed shot-stopper Graeme Smith and opted against extending Czech goalkeeper Jakub Divis' loan from Slovakian side Tatran Presov.
That leaves just Stack and former Celtic keeper Brown, who made 28 appearances last season, as the two contenders for the gloves, with 18-year-old Welshman Calum Antell in need of first-team experience. Calderwood said: "We've got two experienced first-team goalkeepers and the competition was there last year and will be there this season again.
"I think we were in a very fortunate position on a number of occasions last year with the depth of our goalkeeping talent.
"This year it's all about those two competing for the starting jersey week after week, but I'm very secure and happy that we have two quality goalkeepers in our squad."
Calderwood is looking to farm out former Swindon Town player Antell.
"We hope to give him experience by getting him on loan very early, and I think that will be a benefit to him," Calderwood said.
• Falkirk's Scottish Communities League Cup game at Albion Rovers on Saturday, 30 July will be an all-ticket affair with the crowd figure set at 1,100. Tickets costing 14 for adults and 9 for concessions will be equally divided between both clubs when they go on sale next month.