The Dortmund star believes the Liga leader is the front runner to win this year's tournament but his club, which has not lifted the trophy since 1997, has a good chance.
The Blaugrana drew their quarterfinal first leg 2-2 away to Paris Saint-Germain while Reus' side drew 0-0 in Spain against Malaga.
Barca looked as though the club was going to become unstuck against a resilient Milan side in the last 16, but the 23-year-old insists the Catalan giant has demonstrated that the team has what it takes to win the prestigious trophy.
"Barcelona play really good football. They're capable of creating much space, even against teams who defend with 11 players,” he told Die Welt. "Therefore, Barcelona are the favorites to win the Champions League."
The Germany international added that his team is one of the most difficult to play against and, given its results in the competition so far, could go all the way.
"[However,] we're the most unpleasant opponent. We play attractively and offensively," Reus continued. "We're still unbeaten in this Champions League season. That says a lot. But we haven't achieved anything yet and want more."