You've a simple case of vertical convergence there. I've not read every post in this string and this point may have been covered already; if not; here are a few tips:
Expect distortion when using wide angle lenses – especially with architecture. Look into a tilt / shift lens for shots like these. If a set of these expensive fixed focal length lenses isn't within your budget; use what you've got and utilize post processing to repair the flaw. The leaning or vertical convergence in your photo is a very simple fix in any image editing program allowing you to cut and paste the image and adjust the perspective. No special plug-in or stand alone program is necessary. I copied this shot, and put exactly 30 seconds into the repair shown below. If it’s not dead on; it may of course be tweaked to perfection from the original file. I cut the entire image from its background. Next, I pasted the image to a separate layer. I then adjusted the perspective of the shot by eye until it looked acceptable. Remember to crop the image to remove the extraneous background which will be showing along the vertical borders after this adjustment. You'll need to sharpen things up as well as a final step. Definitely shoot RAW for scenes like these; you will have much more information which with to work for the final product.
Good Luck,
Movick
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