Sherman @ CB, and Earl Thomas & Chancellor @ S are all very good. Behind those 3, the rest of the CB core is decent but nothing great. The 3 may be able to shut down 3 of the Broncos receivers fine, but when they have four top quality receivers (J Thomas @ TE and D Thomas, Welker and Decker @ WR) they will struggle to contain them all. Not to mention Moreno has proved to be a good receiver out of the backfield. Throw in the fifth and sixth receiver options for the Broncos in Caldwell @ WR and Tamme @ TE and these guys are definitely better than the fifth and sixth DB's the Seahawks have.
It will be a tough game, but Manning will find a way to still put up some yards. I think the difference in the game will be who wins the battle between the Seahawks Offense and the Broncos Defense. If Seahawks win I can see it being behind the Lynch pounding the ball and limiting the amount of time Manning and the Broncos are given.