Hello, your idea to reconstruct this scene with Photomerge is not bad, but some corrections are needed here: correct the light (in some areas the photo is darker and in other areas lighter). Before you use Photomerge you have to assure yourself that you have the same light conditions in the photos you want to merge. Once merged you have to correct the prospective. Photoshop has different tools to do this, the easier is Distort tool.
Canon EOS 5D Mk II and various Canon lenses L series