My daughter was very much this way, and as much as she and I butted heads when she was 2 and 3, it was still all about mommy. I found that by making a big deal of her giving him a hug or sitting on his lap, she'd do it more often in order to get my approval and then fairly quickly she did it just because she wanted to. Try saying things like "aw, that's so sweet! Hold on, let me get my camera!" when she cuddles with him.
I also agree with having him be the in-charge parent more often if that's not something he does. It was important for my daughter to realize that daddy took just as good care of her as mommy (and was quite often more fun cuz he didn't worry about silly things like dishes or vacuuming!) She couldn't realize that if I was always around and as a SAHM, I pretty much always was. My husband also started taking her on little outings, to the park or the movies, and that helped a lot.
She's almost 6 now and while I'm still the one she seeks out if she's hurt or ill, she adores her Daddy and gives him an even share of her kisses, cuddles and playtime.
Good luck!
M.