Straight from the press, citizens of Movieville:
The intention is to bring back Jim Carrey and Jeff Daniels as Lloyd Christmas and Harry Dunne, the lovable dimwitted pals with big hearts and small brains. Sean Anders and John Morris have been hired to write the script. They co-wrote the Anders-directed Sex Drive and just co-directed the Adam Sandler comedy I Hate You Dad. The hope is for the Farrelly Brothers to direct this next.
Not only this, but to further solidify these plans, Carrey himself has dropped hints:
While Carrey isn’t a big sequel guy, he dropped hints about the movie while he was out promoting Mr. Popper’s Penguins.
This would work provided both Carrey and Daniels were on board for this, because let's be honest- Dumb and Dumberer wasn't exactly a great addition to the franchise, but like the article linked above says, it didn't exactly kill it, either.