When compared with the constant aperture Sony E 10-18mm (equivalent to a extremely handy 15-27mm) f/4 OSS mounted on the 24-MPix NEX-7 the Canon achieves the same overall DxOMark rating of 14 points.
However, the Canon is sharper and has better uniformity. Constant aperture lenses like the Sony are more suitable for video recording (avoiding the changes required to exposure during zooming), not only that it has better light gathering capabilities at the longer end, equating to close to +1EV.
Given the extreme field of view of the Sony, it is perhaps unsurprising that the Canon has slightly lower levels of CA and vignetting. While the ultra-wide Sony is the more attractive proposition for it capabilities it is some $400 more expensive.