The iPhone's software, on the other hand, is doing some auto-adjustment before the file hits the SD card. It's optimized for a decent photo without any manual steps.
Also, notice the distortion in the iPhone photo: the buildings "lean" towards each other. The Canon 24-70mm f/2.8 is a _nice_ piece of glass, and is worth every penny of its $1500 asking price.
tl;dr: Take the 5D shot (in RAW, hopefully) and let a pro have a shot at it in Lightroom. That's a fair comparison.