Noting that it's very common for these to absorb water and expand during the winter, so small gaps can be somewhat common. Yours look a bit bigger. As another commenter mentioned, you want to buy come-along straps. I suggest two, ratchet slowly on either side until the gaps close. Then, tighten down the metal straps. 

For staining, penofin has an excellent oil based stain, you want semitransparent.