Well you should give your specific stats and such so that the dietary gurus can help you but here is my general response to the "sort of" mixed messages I am getting (this may just be lack of info). Edit* Sorry, I see you gave your weight and height. Others can ask for whatever else.
You say you want to achieve a six-pack. You want a lean body. Well you can get that with diet. Or diet and activity (cardio, whatever). As for "lean cut" there needs to be some muscle in order for it to look cut. I've seen cut looking marathoners before but the muscles are so wasted and tiny I think they'd look better un-cut.
Unless you are severly overweight (you're obviously pretty light) I would suggest you put on some good muscle before you cut and then try to actively maintain that muscle while you cut. It is very difficult if not impossible to do both at the same time, i.e. lose fat and gain muscle both at once. However, more muscle makes it easier to cut and makes the outcome look much better.
I hear the "I don't want to be bulky" a lot. Really, really, not something you need to worry about unless you have some really freaky muscle building genetics. You'll have lots and lots of time to decide when you are satisfied before you ever get "bulky". And yes, that includes big muscles with a lot of fat over them too.
I don't know why you are concerned with gaining weight as such. Yes muscle weighs more than fat but it's good weight. As a matter of fact, losing weight should be removed from the vocabulary and only losing fat should be used. We don't want to lose muscle. Even non bodybuilders. It's not good for us.
The answer is to eat enough of the right foods combined with a weight training program in order to build muscle. Hopefully you can do that with a minumum of fat gain. If not, once you get some mass, you cut back the calories while continuing to workout to maintain muscle and lose the fat. There are lots of specifics that go into it, but thats the gist.
As far as Ryan Reynolds body. You can't have it. Even thinking of it in terms of the general look or the degree of cutness is a waste of energy and will only screw you in the end. You can only have your body so you have to work to make it the best you can. One final thought is to not look to guys in movies as your model. A lot of times it's their job to look like that. It's a snapshot. You know for the movie Daredevil Ben Affleck had a personal trainer so he could look better in the suit and have a six pack. You think Ben has a six pack now?