Liverpool
3-4-3: This has been Liverpool's go to formation for most of the season, since they have struggled with four at the back earlier this season. They used this formation the last time they faced off with Manchester United at Old Trafford. Primarily, they've used two actual centrebacks (Lovren and Skrtel mainly) and dropped Emre Can to back in the centreback. This formation has been working wonders for the Reds lately as they are thriving and keeping clean sheets. On the wings, Liverpool mix it up as they could use either players that play left/right back such as Manquillo and Moreno or wingers like Sterling and Markovic. In the middle of the park while Gerrard has been out, Henderson has taken over the role of captain and has done it well with Joe Allen or Lucas Leiva pairing up with him. The front three is what poses the most danger for Manchester United because of their pace, ability to take the defender one-on-one, and their flair. Philippe Coutinho will be on the left, Daniel Sturridge striker, and Raheem Sterling will be on the right wing. Sturridge has finally come back after a series of injuries and will be relishing to get at their Northwest rivals.
3-4-2-1: The same idea as the 3-4-3 except Sterling and Coutinho are in more central roles. They would be playing in-behind Sturridge and just in front of the Allen and Henderson. This might be a little better tactically because with a 3-4-3 the wings of either side could get crowded with a left/right midfielder and a left/right winger sharing the space. With this formation, the left/right mid can attack like a winger with the potential to lay it off to one of the attacking midfielders.
Manchester United
4-2-3-1: This is the formation Manchester United used last week in their finest display of the season against Tottenham. With this formation, United can get a nice balance of attack and defence. For awhile now, Louis van Gaal has scrapped the three/five at the back formation, experimenting with formations. This has produced the best result so far. With what is expected to be the same of nearly the same lineup as they played last weekend, expect Carrick and Herrera to be influential in the holding midfield roles to linkup play as these two get it going with smart passes or deciding to not pass and keep dribbling to hold up play. There are three attacking midfielders, Young, Fellaini, and Mata, in this formation, but Fellaini is expected to drop back a little more due to his physical presence and provide linkup play between the holding midfielders and the attacking midfielders. Wayne Rooney is expected to be the lone striker, but as we all well know, this man will do everything for United from tracking back on defence, making tackles in the midfield, to scoring goals.
4-4-1-1: Van Gaal may use this formation if he is feeling a little defensive-minded this weekend on their trip to Anfield. Young and Mata would be more like left and right midfielders in this sense with the responsibility of tracking back to help on defence. Fellaini would be playing right behind Rooney with United trying to send the long ball to him to win in the air to get it to Rooney.
4-3-3: This is the last possible way United could lineup with the predicted lineups. In this formation, Fellaini would drop back into the midfield three along Carrick and Herrera. This would give United a little more fluidity with three midfield players to get the ball up to the wingers and striker.Young would occupy the left wing while Juan Mata would occupy the right wing. Although this would bring more fluidity, putting Juan Mata out on the wing would not be the best choice because he's not comfortable out there and does not have the pace to be a winger.