Labuschagne, who only has 10 T20 matches at domestic level under his belt, rattled off a 50-ball century in the second of two matches on Tuesday while Stoinis struck 68 off 37 balls to add to the 87 he made in the 50-over practice game at the weekend.
Few would bet against Labuschagne eventually earning a T20I berth given his last 12 months at the international level - coach
Justin Langer spoke of the "acceleration of his improvement" - but both he and Stoinis, who had a prolific Big Bash last season opening the batting for the Melbourne Stars, won't be dislodging the current top three of David Warner, Aaron Finch and Steven Smith.
"We've had a pretty settled T20 side over the last 12 months or so and all we can ask for is that guys bang so hard they are putting pressure on the guys in there," Langer said. "So, whether Marnus plays this series or not, or certainly the first game on Friday night, time will tell. We haven't decided that yet. But he's certainly done, as has always been the way since coming into international cricket, everything he possibly could. He was hitting Pat Cummins, the world's best, over point for six."
One option for Stoinis, who has not played for Australia since last year's World Cup, would be to return in the middle order. He also provides a solid bowling option with his medium pace, but Langer believes his best position in the format is opening and labelled the Warner-Finch pairing as the best white-ball first-wicket combination in the world.
"He certainly won't displace them at the moment," Langer said. "I think he is an outstanding top-order player, it gives him a lot more time, he's got incredible power. We also know that he is an adaptable player, and he can play anywhere but I feel he is [best] in the top order. When an opportunity comes time will tell. He is doing everything in his powers to be knocking on the door for selection."
While knowing that Australia will lack some match "hardness" heading into the series having not played since March - against an England side that has been in action for two months - Langer was comfortable with the lead-in the squad had managed. However, he acknowledged the challenge the home side will pose, particularly having brought back some first-choice players who had been on Test duty.
The T20I series will pitch the top two-ranked sides together, but in ODIs there is a considerable gap from England in top spot to Australia in fifth.
"Dangerous, that's what I made of England," Langer said having followed the T20Is against Pakistan. "I've watched the way Eoin Morgan plays, it's exciting to watch, he just comes out and smacks it from ball one. They've got some good young players, we've seen the squad, they've brought some of their more experienced players back. They've been the best one-day team in the world for a few years now. We know what to expect."