Looking at the 3 games for each team, they progress like this, with each series being Saturday-Tuesday-Saturday.
Dallas
hosts Colorado
hosts New England
at NYCFC
New England
hosts NYCFC
at Dallas
at Montreal
Both teams are probably more likely to rest players for the first game given that there are only two days' rest between that one and the US Open Cup Final, which is the most important game of each bunch. Problem is that those first games are each very important for the regular season.
Dallas is hosting the 2nd place team in the West, which is 8 points back, but has 2 games in hand. Perhaps they will take the position that their lead in the West and SS races is big enough to rest players for this one.
New England is just below the playoff line, and all the teams around them have games in hand. They need to get 3 points out of their game against us rather desperately as their next two MLS games are on the road. Still, perhaps they take the reasonable approach that Tuesday represents their only realistic chance at a trophy - certainly more likely to win that one than even make the playoffs, much less win the playoffs.
My guess is that each team rests some players on Saturday, goes all out to win on Tuesday, and then plays their regular guys on the following Saturday. We will see how it goes.