Looking at your character, the hard part wont be poser (though it may be harder then you expect) but actually getting your 3D character to match the look of your 2D sketch properly. Do you actually need a full 3D character though ? Like will your game camera be rotating around your character in full 3D, or is he just gonna be shown side-on like in the skecth ? Cause if it's the latter, you could get away with just pasting the sketch/drawing on a flat 2D polygon and animating as needed.