The Black Cats face Johnson's former employers Manchester City in the final of the competition at Wembley on Sunday with Manuel Pellegrini's men currently sitting in third place in the league table, three points adrift of leaders Chelsea but with a game in hand.
He has no doubts about the quality of the opposition he and his team-mates will face this weekend, but having played in City sides which have at times struggled to beat Sunderland, does not fear the challenge.
Johnson said: "For me, they have the best squad in the league by far and it's going to be difficult, we all know that.
"But we have beaten them once already this season and we have had quite a good record in recent years against them.
"I remember being in the City side a few times coming here and struggling, so hopefully it will be like that again.
"We all know it's a massive, massive task for us, but it's a cup final and so many times over the years, it's not as simple as everyone expects it to go."
Sunderland have, in fact, beaten City on each of their last four league visitors to Wearside, and came within five minutes of a famous victory at the Etihad Stadium in March 2012 when goals from Mario Balotelli and Aleksandar Kolarov snatched a draw for the home side.
Johnson, who was introduced as a half-time substitute by then manager Roberto Mancini in that game, joined the Black Cats in a £10million switch around five months later as owner Ellis Short spent big in a bid to end the club's seemingly perennial fight for top-flight survival.
The England international showed only flashes of his undoubted talent during his first season back in the north-east, but has blossomed once again under new head coach Gus Poyet to the extent that he scored seven goals in as many games in January and February.
Johnson's improvement went hand-in-hand with Sunderland's climb from the foot of the table, but he insists there is no secret to the progress made both individually and collectively.
He said: "It's just been down to hard work for both. It hasn't been one thing with me personally.
"With the team, we have been working on all sorts of different things really - our shape, our attacking, defending off the ball.
"We have just been slowly putting it together piece by piece and it has started to show in our performances.
"It's just been down to working hard on the training ground, really, because we have the players. It was just getting that out of them."