The Serie A leaders travel to the Bundesliga leaders on Tuesday, with Bayern hoping to go one better than last season when they were beaten by Chelsea in the final of the competition.
However, Appiah has backed Juventus to inflict more heartache at the Allianz Arena.
He told Goal.com: "It's going to be a difficult game, with two big clubs who are doing well, but I think each of them would use their home game as an advantage.
"I will go for Juventus to win 2-1, although Bayern are looking scary, but they are an odd team and I believe strongly that Juventus will go through over two legs."
Appiah made 48 appearances for the Old Lady before departing in 2005.