Pep Guardiola confirmed that Trafford will keep his place in the Man City side for the final against Arsenal.
That followed City's 3-1 semi-final second leg win over Newcastle United, which sent them through 5-1 on aggregate.
Trafford is understudy to Italian star Gianlugi Donnarumma in the Premier League but has been given his chance in cup competitions by Guardiola.
The keeper from Greysouthen will now get the chance to win a major domestic trophy with City, after making a number of saves in the second leg at the Etihad Stadium.
Trafford will start in the final against Arsenal, says City boss Pep Guardiola (Image: PA)
“I said from the beginning James is a top player, a top-class keeper, so he’s got an incredible future ahead of him," said City boss Guardiola, who signed 23-year-old former Carlisle United academy keeper Trafford from Burnley for a second spell last summer, before the club then moved for Donnarumma from Paris St Germain.
"The position of keeper is special because of course he has to play.
“Some players like Nico O’Reilly can play left-back, attacking midfielder, in the pockets, holding midfielder but the keeper has to play keeper and there is just one of course.
“He’s an extraordinary keeper and I’m really pleased.
"With the final, he’s going to play the first final of Carabao Cup for him, and in FA Cup of course everything can happen."
Two goals from Omar Marmoush and a Tijjani Reinders goal, all in the first half, saw City dismiss any danger of a fightback in the semi-final by holders Newcastle, who got a second-half consolation through Anthony Elanga.
The will face Arsenal in the final after the Premier League leaders won their semi-final against Chelsea 4-2 on aggregate, following Tuesday's 1-0 second-leg victory.
The League Cup final will be played at Wembley on Sunday, March 22.