The two teams head into the match on level terms after the Robins were pegged back by a late penalty in the first leg on Saturday.
McCormack said that has added fuel to the fire and is confident of reaching Wembley should his teammates produce their best.
"We will show them respect, but we will take the game very seriously," McCormack told the club's official website. "Things can change at the flip of the coin, we know that, but it's a match we will look forward to.
"The end of the game made me more determined and angry to go and get the win on Monday. Brentford have to come out and beat us on Monday, but we know we are good on the counter-attack.
"If we can get to our best, then we can produce the goods and I'm sure we will do it."
Sheffield United lead Yeovil Town by one goal in the other League One playoff semi-final.