Guptill, who has been sidelined by a hamstring injury, will be undergoing a fitness test and upon clearing it, will be in fray to play as an opening batsman.
Allen finished as the Super Smash's highest run-getter, scoring 512 runs. He will be a direct replacement at the top of the Black Caps line-up should Guptill fail a fitness test in Christchurch this week.
"Finn's been in outstanding form and he's certainly an exciting talent," selector Gavin Larsen said in a statement.
"Martin's our incumbent opener and our highest T20 international runscorer so we're backing him to do the job at the top of the order, but he will need to prove his fitness, and it's good to know we have a ready replacement in Finn on standby."
New Zealand T20I squad: Kane Williamson (c), Martin Guptill, Tim Seifert, Devon Conway, Glenn Phillips, Mark Chapman, Jimmy Neesham, Mitchell Santner, Ish Sodhi, Kyle Jamieson, Tim Southee, Trent Boult, Hamish Bennett, Finn Allen (standby)