The Union's Jack McInerney leads Major League Soccer with eight goals for fifth-place Philadelphia, while fourth-place Montreal's Marco Di Vaio is among a group of three players with six goals, although the Impact striker has played two fewer games.
The five-foot-10 McInerney, a 20-year-old known as Jack Mac, is having a breakout season in his third year as a pro since he was drafted seventh overall out of high school in 2010 by the Union.
His speed around the goal and ability to get open is similar in style to the 36-year-old Di Vaio, who is listed at five foot 11.
McInerney will likely be a handful to veteran Montreal centre backs Alessandro Nesta and Matteo Ferrari.
"It's important that our defence marks him well because he's doing very well," said Montreal midfielder Patrice Bernier. "He has good movement and he's very fast.
"It will be a difficult game for Alessandro and Matteo. We'll need to play a strong game. They've won three times away, so it's a dangerous team."
Philadelphia (5-4-3) has been hard to read this season, going 3-2-1 away and 2-2-1 at home. They are coming off a three-game stretch in which they lost 4-1 at home to Los Angeles between a pair of 1-0 wins over Chicago.
The Impact (6-2-2) are 4-0-1 on home turf. In their last MLS outing at Saputo Stadium, they pulled out a 3-2 win over Salt Lake on May 11 on late goals from Di Vaio and Ferrari.
Nesta is due to return from a nagging adducter injury to bolster the central defence, but questions remain for the fullbacks.
Jeb Brovsky, who along with goalkeeper Troy Perkins has played every minute of every game this season, is a question mark after breaking his nose in six places in a 0-0 draw with Vancouver in Voyageurs Cup play on May 15.
Fullback Hassoun Camara left practice early on Thursday for reasons unclear, while Maxim Tissot of Gatineau, Que., who made his first MLS start at right back against Salt Lake, is out for two to three weeks with a fractured toe.
Brovsky got patched up and finished the game against the Whitecaps and then went for surgery. He trained this week in a face mask, although he had to clear it of fog with a towel at intervals.
Coach Marco Schallibaum called Brovsky a warrior. That got no argument from Bernier.
"It looks a bit awkward, but Jeb is a guy who is not going to quit," Bernier said. "You could see when he broke his nose he wanted to get the operation right away.
"Some people would have missed three or four weeks and he's already available to play on Saturday. It might hinder him a bit, but not enough to affect his play. He may have to wipe the fog off on the sideline, like a hockey player."
Schallibaum expects Camara to be ready, and Dennis Iapichino is available at left back.
The Impact were on a 10-day break in their schedule, which was useful as midfielder Felipe Martins recovered from passing kidney stones.
Schallibaum does not announce his starting 11, but from practice this week it appeared he would stick to his recent preference for a two-forward lineup, pairing Andrew Wenger with Di Vaio even though the two have shown no chemistry.
Forward Daniele Paponi, Di Vaio's former Bologna teammate, is out with a hamstring injury along with midfielders Andrea Pisanu (hamstring) and captain Davy Arnaud (concussion).
The Union will have defender Jeff Parke, their off-season acquisition from Seattle, back after he missed three games with a sore hamstring. His return allowed them to trade defender Bakary Soumane to Chicago this week for a second round draft pick and allocation money.
Up front, McInerney teams with veteran Sebastien Le Toux, who is back in Philadelphia after splitting last season between Vancouver and the New York Red Bulls.
"They're a very solid team," Di Vaio said of the Union. "They won three games away, so that must help them here, in the head.
"They have good strikers. It's not an easy game."
Note: Forward Sanna Nyassi has been called in by Gambia's national team for World Cup qualifying games against Ivory Coast and Morocco and will be away June 3-17. He will miss a game June 15 against Columbus.