McCarthy-Matt Flynn will be the starter. He's taken all the starter's reps this week. #PackersTolzien has shown some promise but Mike McCarthy can't wait for him to figure it out while their playoff chances slip away. Based on their last game, it's a no-brainer that Flynn should be starting. Vince Verhei wrote earlier this week "that Matt Flynn needs to be in Green Bay, and Green Bay, at least now, needs Matt Flynn."
— Green Bay Packers (@packers) November 27, 2013
And if the Packers beat the Lions, it will be because of him. While I'm a fan of RB Eddie Lacy, the Lions have the 2nd best run defense according to Football Outsiders. Last week, RB Bobby Rainey, who started a fantasy stampede after rushing for 163 yards against the Falcons on November 17th, was held by the Lions to 35 yards on 18 carries. Lacy can be the offensive focal point against a terrible run defense like the Bears, but he's not going to be a big factor against the Lions.
The good news is that the Lions' pass defense is ranked just slightly ahead of the awful Vikings, and Flynn did well against them last week. Now he's taken all the starter's reps (see tweet above) and will have the advantage of playing inside. The Buccaneers burned the Lions deep on a couple of play action passes and that's something the Packers will have to exploit too.
However, QB Matthew Stafford is having a very good season. He fell apart last week with 4 INTs but he's only got 12 for the entire season. Also, WR Nate Burleson returned last week, and Stafford could find himself on pace for another 5000+ yards and 40+ touchdown season. The only thing that slowed him down in 2011, the last time these two teams played on Thanksgiving, was that he threw 3 INTs. However, the 2013 Packers defense has only recorded 4 INTs in their first 11 games, so they'd be lucky to pick him off even once.
Unless Flynn has a repeat of his game against the Lions back on January 1, 2012, when he threw for 480 yards and 6 TDs against them at Lambeau, I don't see how the Packers are going to keep up in a shootout. The Lions are probably going to score over 30 points and the Packers haven't scored over 30 points since QB Aaron Rodgers broke his collerbone. The upset is possible, but Flynn and the Packers' defense would have to play their best games of the season to make it happen.