Argentina vs. Canada: 5 players who will define Copa America semifinal

Here we go again. Canada gets a second shot at Argentina on Tuesday night at MetLife Stadium, where Jesse Marsch's ascendant side seeks the most consequential win in the history of the men's program to reach the Copa America final.

The Canadians, reinvigorated under Marsch, showed they could trouble Lionel Messi and Co. before eventually succumbing to a 2-0 defeat in the tournament opener last month. Can they send shockwaves throughout world soccer by returning the favor and ousting the reigning world and South American champion? They certainly think so. How these five players perform will shape the outcome of the anticipated rematch.

Jacob Shaffelburg

Maxime Crepeau has been one of the best shot-stoppers at Copa America. Derek Cornelius has eased long-standing concerns over the country's lack of quality center-backs. Tani Oluwaseyi has provided a spark off the bench every time he's stepped on the pitch. But no player has rocketed to prominence in the past two weeks quite like Shaffelburg, Canada's "Maritime Messi" who has become a pillar of Marsch's team in the blink of an eye. The Nova Scotia native, who started the first two matches of the tournament on the bench, forced himself into the starting lineup with his dynamic play and scored the biggest goal of his career in the quarterfinal victory over Venezuela.

The rapid 24-year-old is now an undisputed starter and one of Canada's most dangerous attacking threats. He leads the team in goal contributions and sits third in progressive carries, always providing an outlet who can flip the field in an instant with his speed and direct running style. His expected assisted goals total (1.6) is third best in the entire tournament - behind only Messi and James Rodriguez - despite starting just two games. If Canada is to pull off the upset, Shaffelburg will need to be a central figure down the left flank, which matches up with Argentina's most vulnerable area on the field.

Lionel Messi

Lionel Scaloni has had unprecedented success in taking the burden off Messi and spreading the responsibility around. Argentina is less reliant on its iconic captain than ever before, and the team is clearly better off for it, winning its last two major tournaments and sitting just two games away from claiming another. That's been particularly important at this Copa America as Messi, 37, has been hampered by a leg injury that forced him to sit out one game and made him look human in the others; he missed two clear breakaways against Canada in the group encounter and struck the crossbar with a Panenka attempt in the shootout after a subdued quarterfinal performance against Ecuador. This isn't peak Messi. Not even close.

But despite the irritating muscle issues, the shoddy playing surfaces that have been a blight on this tournament, and his advancing age, he's still Argentina's undisputed talisman. Of course he is. Even having missed one full match, Messi still leads the Albiceleste in expected assists, key passes, passes into the penalty area, and shot-creating actions in the competition. He's yet to score a goal of his own, but he's still thriving as a creator. Lose sight of him for even a second, as Canada fatally did twice at Mercedes-Benz Stadium last month, and he'll punish you.

Alphonso Davies

Some of Canada's brightest moments in the tournament-opening defeat came courtesy of Davies doing what he does best: racing forward from his nominally defensive position and beating his man before cutting the ball back across the penalty area for a teammate. It's simple enough - get one of the fastest, most explosive players in the world one-on-one against an isolated full-back - but it can be devastating. Rather than making him one-dimensional, that lucidity has actually helped Davies, who had previously been given a free role with the national team and could get stuck trying to do too much on his own.

"I've been incredibly impressed with him," Marsch told reporters ahead of Tuesday's match. "Most importantly for me, (giving him the captaincy) actually created clarity in the way he's played. He doesn't feel with this team now that he has to make every play. ... He doesn't need to be more than what he is. We just want him to be the player that he is, and we want him to be the leader that he is."

Emiliano Martinez

If you can limit Messi's impact, and you can also keep tournament-leading scorer Lautaro Martinez quiet, and you can fight off Cristian Romero and Lisandro Martinez to create chances, you still have to find a way past "Dibu." Argentina's goalkeeper and chief showman has been in typically inspired form this summer. He's conceded just one goal, but more than that, he's bailed out his team when it mattered most in critical moments. He denied Eustaquio's point-blank header when Canada and Argentina were still tied in the tournament opener; he made two smart saves diving down to his right against Chile before his side grabbed a late winner; and he got his team back on track after Messi's shocking penalty miss in the quarterfinal shootout against Ecuador, turning aside the first two spot-kicks he faced - including an outrageous one-handed parry that spurred Argentina to victory.

"He gives us a lot of security and peace of mind. We try to do the same for him, but in these important moments he's always there, he's always there," Rodrigo De Paul said of his netminder after the aforementioned shootout win. Canada proved that it can cause headaches for Argentina when the two last met. But the Canadians, like many others before them who have been felled by the South American powerhouse, couldn't beat Martinez. Whether in normal time or from 12 yards, they need to do exactly that to reach the Copa America final and claim the biggest win in the program's history.

Stephen Eustaquio

It's a cliche, sure, but controlling the midfield battle remains paramount to success. That can take many forms - simply owning possession doesn't necessarily equate to "winning" in that area of the pitch - but if Canada is going to unseat Argentina, Eustaquio is arguably the most critical piece of the puzzle. "Steph is mentally maybe our most mature, careful, clear, secure person on the team. It would have been easy to make him captain as well because of those things, because he's a rock. … He kind of goes unnoticed sometimes, but he's clearly one of the most important guys in this whole project," Marsch said.

Canada's vice-captain will have an even more difficult task than he did in the first meeting between the two teams. Barring a surprise, Enzo Fernandez, who didn't feature in that game, will start over Leandro Paredes in Argentina's three-man midfield alongside De Paul and Alexis Mac Allister. Fernandez is more mobile than Paredes and is comfortable joining the attack, whereas his compatriot prefers providing incisive passes from deep. Together with Mac Allister, who had success against Canada on June 20 with undetected late runs into the penalty area, Fernandez offers another credible scoring threat. Whether Eustaquio is partnered by Jonathan Osorio or Ismael Kone, Canada's midfield conductor will have more to think about this time around as he tries to command the center of the field, balancing his defensive duties with his responsibility as a tempo-setting passer.