I think the Packers' secondary is better than San Francisco's. If GB can pressure Favre with the blitz, he might not have the same success as he had against San Francisco. From what I understand, Favre was very mediocre until the final drive of that game. He threw over 300 yards, but 60 of that was on the final drive when San Fran got very laid back. So 240, 1 TD, and 1 INT for example is solid, but not ridiculous.
I haven't watched the game though.
The key to the game is still to stop Adrian Peterson. If he runs wild, won't matter how good Favre plays or how poorly he plays.
As far as his history against the 3-4. He lit up San Diego in 07 and they run a 3-4. If you want to go way back go back as far as Carolina vs. Green Bay for 96 Title. Carolina's head coach was Dom Capers and they ran the 3-4. Favre threw 292 for 2 TD's and 1 INT. Following year they met late in the year and Favre threw 3 TD's for 256 and another INT.