The clubs met on Saturday with the Hornets recording a 3-1 victory against a City team which will differ from those on view tonight.
Academy Director Steve Ogrizovic is relishing the tie and told Sky Blue World: "Watford are going to be difficult. "They’re in our section and they beat us on Saturday, although we didn’t play our full side.
"They’re going to be tough and we’re under no illusions that we’ll have to play very, very well on the day and if we can do that I think we can turn them over. If we’re anything short of that then it will probably go the other way."
"The team itself has done well this year and they’re up for it. You can see there’s an extra spark, an extra spring in the boys’ step and the game can’t come quick enough."
City have twice got to the final in recent years losing to West Ham and Arsenal and last season went out in the fourth round on penalties after a 1-1 draw at Nottingham Forest.
Kick off at Vicarage Road is at 7pm and there is extra time and penalties.
Admission is £3 for adults and £1 concessions.
M1 Junction 5 and take the new road (A4008) towards Watford town centre. On to the ring road and follow signs for Watford General Hospital. The ground is next door.
Watford Junction station 1.5 miles Watford tube 20 mins walk