Music: {allcanada} ALS, ARGOS GO WITH BACKUP QBS TO OPEN HOME-AND-HOME ON TSN

TORONTO - Under normal circumstances, it would be an East Division showdown between two veteran quarterbacks who've won multiple Grey Cups and compiled Hall of Fame credentials.

But with Anthony Calvillo and Ricky Ray both ailing, it will be backups Tanner Marsh and Zach Collaros in the spotlight tonight when the Montreal Alouettes visit the Toronto Argonauts at Rogers Centre to kick off an important home-and-home series.

Watch the game live on TSN and TSN Mobile TV, or listen to it on TSN Radio 1050 starting at 7:30pm et/4:30pm pt. You can also catch live action, social interaction and in-game stats with TSN.ca's live GameTracker.

Between them, Ray and Calvillo have combined to throw for more than 120,000 yards and over 600 TDs while winning three Grey Cup crowns apiece. But Ray is out approximately six weeks with a shoulder injury while Calvillo is recovering from a concussion.

That means Marsh, 24, will make his first CFL start for Montreal (3-5) while Collaros, a 25-year-old sophomore, will start just his second game for Toronto (5-3).

"That's been the trend in the CFL this year, there's been a lot of teams that have had to face that adversity," said Jim Popp, Montreal's GM and interim head coach. "There's been a lot of injuries in our league this year . . . it's going to happen at times and when it does you have to throw them in there and go at it.

"It's not just the quarterbacks, it's the attitude your team has when they go on the field and have to play with them."

Despite their relative inexperience, Marsh and Collaros have led their teams to impressive wins this season over the B.C. Lions.

Marsh's clutch 57-yard completion to Eric Deslauriers set up Sean Whyte's game-ending 15-yard field goal to cap a thrilling 39-38 win over the Lions on Aug. 22. Marsh replaced starter Josh Neiswander and was 14-of-32 passing for 329 yards and a TD but threw four interceptions and lost two fumbles.

"When you have somebody who's gone through the adversity he went through earlier in the game and was able to come back and throw a strike like that, of course you have confidence in him," said Alouettes veteran linebacker Chip Cox. "It's like no matter how far down or how bad the game is, he's going to be able to brush it off and come back and do his job and deliver."

On July 30 with Ray (knee) out, Collaros was 21-of-25 passing for 253 yards and three TDs in a 38-12 home win over B.C. Collaros came on in place of Ray in last week's 35-14 home loss to Calgary, completing 16-of-26 passes for 221 yards while surrendering Toronto's first interception this season.

"I think he's got some natural leadership abilities, kind of a fiery guy, football is important to him," Toronto head coach Scott Milanovich said of Collaros. "I just like his makeup."

Both offences lose experienced starters but their young replacements certainly bring a different dynamic to the table. Collaros and Marsh are very athletic and more than capable of using their arms and legs to make big plays downfield.

"It's kind of what we lost, they lost and what we gained they gained," Cox said. "They've got the same thing we've got pretty much in backup guys who can make plays with their legs and down the field also.

"I think we're pretty evenly matched right now."

These next two games are important as Toronto leads the East Division by two points over second-place Hamilton (4-5) and four ahead of Montreal. The Argos also beat the Alouettes 39-18 at Molson Stadium earlier this season and a sweep would not only give the defending Grey Cup champions the series but an eight-point cushion on the Als.

Montreal is expecting running back Brandon Whitaker and tackles Josh Bourke and Michael Ola to play after missing time with injuries.

Milanovich expects Collaros and Marsh to meet the challenge of replacing all-star quarterbacks who've enjoyed plenty of CFL success.

"Sometimes I think when guys replace people like Ricky or Anthony the bar has been set so high they almost have no choice but to raise their level of play than if they were replacing someone who wasn't playing as well," said Milanovich, who spent five seasons as an assistant with Montreal. "I know Zach expects a lot out of himself despite how well Ricky has been playing.

"He (Marsh) is a playmaker . . . particularly the last play (versus B.C.) was a good read to give Eric a chance to make a play with the game on the line. For guys in that situation and quarterbacks the game either speeds up and it gets worse or it slows down and they're able to focus a little better and to me it showed he was able to focus in and kind of slow the game down and go play to play and execute that (winning) drive."

Collaros faces a Montreal defence that's ranked second in fewest yards allowed (316.1 per game) and sacks (27) and tied for third in most interceptions (eight). Cox has a CFL-high 62 tackles while teammate Kyries Hebert is tied for fifth with 42.

"They do a lot of good things," Collaros said. "They pressure the quarterback, that's where it all starts for them and they do a great job of disguising it.

"We're going to have to be able to see that and when they do come, take advantage of it. That's executing the hot routes if they do bring everybody and if they drop out, be able to go through the progressions and get the ball to the right guy."

Milanovich agrees.

"I love how (Alouettes defence) is playing," he said. "They're very aggressive and put a lot of pressure on the quarterback.

"It makes it difficult on a quarterback to get his reads and get comfortable in the pocket . . . we have to do a better job of running the football and taking some of the pressure off Zach but I think he's locked in and we have a pretty good plan for him."

Marsh earned most of the reps last week ahead of Neiswander and former Heisman Trophy winner Troy Smith, although Popp said he'd play all three if required. As for Marsh, a priority will be protecting the football against Toronto.

"No doubt, the turnovers," he said. "You can't turn the ball over four times and expect to win.

"Luckily our defence and team played great last week."

Prior to his injury, Ray was the CFL's hottest quarterback with an 88 per cent completion average over his last five games and is the only starter not to have thrown an interception. Regardless of Ray's status, Cox said the time is now for Montreal to climb back into contention in the East.

"Whether Ricky Ray played or not . . . we have to show up now." he said. "It's time.

"I don't know what my tackle total is, I know we're at 3-5 and we're No. 3 in our division. I'm not used to being No. 3, I'm used to being No. 1 in our division so anything else doesn't matter to me."