Here's what they said about this pick:
Cannon can start on the inside right away, and may be able to replace Langston Walker at the right tackle position, which would allow Walker to move inside and give the Raiders 700-plus pounds on the right side to open holes for Darren McFadden and Michael Bush. Cannon was a terrific part of the success that TCU has enjoyed over the past few years, and he will be a force in the NFL as well.
When you have one of the best running games in the NFL, it's a smart move to keep those offensive linemen fresh. I like this pick for that reason. The Raiders know what their strength is and continue to add pieces to it.
For the full explanation of this pick, check out Mocking The Draft.