The three heavyweights were drawn together in a tough-looking Group F for next year's tournament, with a play-off contestant still to be added.
France and Germany will enter as winners of the past two World Cups, while Portugal are preparing to defend the trophy they unexpectedly won in 2016.
Santos' side were also crowned inaugural Nations League champions in June but the wily 65-year-old coach quickly positioned his team as underdogs.
"It will be a strong group, two favourites and a candidate," Santos told reporters.