This is the biggest regular season series that I can remember in the last 20 years. So much on the line. A nice break to get some rest for Lindor, Alonso, Nimmo, and McNeil would go a long way. Could also allow Marte time to not rush back. He has been missed.
As for Alvarez, this is an audition. McCann is not getting the job done at all. Even his defense has been sketchy. If Alvarez is stinging the ball at DH, he needs to get reps behind the plate in the Nats series. You can still start Nido, who has hit well post all-star break (.290/.319/.449) but you can see what you have. McCann should not be on the postseason roster.