Harper has faced Gore 23 times, with a total OPS of .609. Conversely, Alonso only has 1 plate appearances against Koenig so tough to reliably predict this one. Lean on the other splits on this page.
Weather impact
Heavy wind (blowing out), hot temps, ballpark elevation, etc can all have a big impact on long fly balls. An extra few feet can be the difference between warning track and a 3-run dinger. In Harper's game, our HRForce Index at first pitch is 1.6 (60% more HRs expected). Meanwhile, Alonso will be playing under an HRForce of 1.6 (60% more HRs expected (roof likely open)). With equal HRForce values, ball flight conditions are roughly the same in both games. So, weather's a draw.
Weekly Roster Lock Leagues
For those of you in leagues that require you to set your lineup before the start of each week, day offs can be a bummer. Everything else being equal, give the edge to players that play at least one more game a week. For the M-F week that includes 9/28/24, Harper has 6 games scheduled, while Alonso has 5. So, with one more game, that could make a difference, especially in H2H leagues where you need to pile up points. Slight advantage to Harper.