Looking at the David Cup teams, Russia look to be the big favourites. They have two in the top 5 in the rankings, no other team has 2 in the top twenty. While they don't have a specialist doubles pairing, not all teams do.
Other than them USA look a good team, Italy look strong, as do the UK. Any team with Djokovic stands a chance. Had Zverev played, then Germany would look good but he isn't. Note if Berrettini was fit, Italy would look even stronger.