The Catalan side drew their quarter-final first leg 2-2 away against Paris Saint-Germain, while Reus' side drew 0-0 in Spain against Malaga.
Barca looked as though they were going to come unstuck against a resilient Milan side in the last 16, but the 23-year-old insists the Liga leaders have demonstrated they have what it takes to win the prestigious trophy.
"Barcelona play really good football," Reus told Die Welt. "They're capable of creating much space, even against teams who defend with 11 players.
"Therefore, Barcelona are the favourites to win the Champions League."
The Germany international added his team are one of the most difficult to play against and, given their results in the competition so far, could go all the way.
Reus continued: "[However,] we're the most unpleasant opponent. We play attractively and offensively.
"We're still unbeaten in this Champions League season. That says a lot. But we haven't achieved anything yet and want more."