The Blaugrana drew their quarter-final first leg 2-2 away to Paris Saint-Germain while Reus' side drew 0-0 in Spain against Malaga.
Barca looked as though they were going to become unstuck against a resilient Milan side in the last 16, but the 23-year-old insists the Catalan giants have demonstrated they have 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 favourites to win the Champions League."
The Germany international added that 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.
"[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."