The decision to have the final round of group stage games kick off consecutively rather than simultaneously relieves both these teams of the burden of worrying about whatever Ecuador does or doesn't do against Haiti. Brazil and Peru will know exactly what they need to do to qualify for the quarterfinals - and if Haiti has beaten Ecuador when this match starts, Brazil and Peru will simply be tussling for first or second in Copa America Centenario's Group B.
The most likely scenario, however, is that Brazil will advance with a win or a draw; Peru (since Ecuador is the heavy favorite to beat Haiti) will most likely need to win - an Ecuador win by two or more goals takes the tie away from Peru as an option. We can hope, therefore, for a match which neither side can afford to take lightly.
The surprising finale to Group A - which saw the USA advance as group winner and Colombia unexpectedly slip to the runner-up spot - potentialy makes winning Group B the less attractive option for these teams: each might prefer to play USMNT (home advantage notwithstanding) instead of Los Cafeteros.
But if Ecuador beats Haiti, a draw probably won't suit Peru and losing woould punt either Los Incas or Brazil out of the tournament. It's unlikely that this match will kick off with both teams content to field their reserves and see what happens; even more unlikely that either will have the luxury of trying to lose in order to duck Colombia and engineer a match-up with USMNT (and both Brazil and Peru might prefer the idea of playing a more familiar opponent - Los Cafeteros - on neutral ground rather than having to take on the USA in Seattle).
Whatever happens, USMNT will know who it is playing in the quarterfinals at the end of this match.