The Mets and Pirates were rained out on Monday night, but they will play a traditional doubleheader starting at 4:05 PM on Tuesday. That makes sense, as the Mets are making their only visit of the 2016 season to Pittsburgh right now.
With that the news, both teams will presumably stick to the starting pitchers they had planned on using coming into the series. That'd leave the Mets' starters for the series as Steven Matz, Jacob deGrom, and Noah Syndergaard. And the Mets will presumably face former Met Jon Niese in the first game of the doubleheader.
While a Wild Car spot is not the goal for the Mets this year, it's worth noting that this series is important in that regard. The Mets are currently one-and-a-half games ahead of the Pirates for the top Wild Card spot in the National League. The division should still be the goal, but maintaining a lead on other contenders for the postseason safety net would be preferable.