GK: David de Gea
Earlier in the season, much was made of Sir Alex's decision to not pick a number one goalkeeper, but to instead rotate between David de Gea and Anders Lindegaard. At the time, it seemed a potentially useful decision that would foster the sort of competition that would bring the best out of the two goalkeepers. However, that move coupled with injuries to United's defense meant it didn't work.
The team was conceding a lot of goals in matches and the lack of continuity in goal was highlighted as one of the reasons for that. Of late, Sir Alex seems to have changed his stance—having started David de Gea in United's last eight matches—and it has certainly helped the team.
This match would be an odd time for Sir Alex to change things around, so de Gea should start.
LB: Patrice Evra
Having been rested for United's FA Cup tie against West Ham, Patrice Evra should be fit and ready to take on Liverpool.
Rafael's season thus far has being a revelation in many ways. His skill in the tackle, and his knack for attacking have been a regular feature of United's play this season.
An injury ruled him out of the side for a few games in December, with Chris Smalling deputizing in his absence, but the Brazilian is back at a good time for United and should start against Liverpool.
CB: Jonny Evans
With doubts about Nemanja Vidic's full fitness still floating around, Jonny Evans seems Sir Alex's best choice for the rigors that Liverpool will bring. However, Vidic started against against West Ham in the FA Cup, and may well be picked to start this match.
CB: Rio Ferdinand
Rio Ferdinand was rested for the FA Cup, and I believe it was with the Liverpool game in mind. Barring injury, it would be a pretty big leap of faith to start Vidic ahead of him, so Ferdinand to partner Evans.