You can not take images from 1 that is pretty much from Raw and compared to another that is upsampled by close to 30% and expect to make a true judge of sharpness.
Sure you can. All you have to do is decide ahead of time what 'conclusion' you want your 'test' to show, and then design your test accordingly.
I can understand some of the initial premise of the upsizing, i.e. showing the same size crop so the size of an object shown in the crop is the same size, but this just does not work.
If anything, what it tells me is either:
1) The author is intentionally being deceptive
- or -
2) They really do not understand digital files, resolution and comparison.
To me the proper way of doing this comparison has to be raw to raw with an understanding that the the Nikon image will obviously be blown up a bit, but looking at a 500 x 500 pixel representation of the Canon Raw and then comparing to the Nikon Raw, one can look at the edges, CA, noise, etc.
By the same token, another poster raised an excellent point that the lenses used will also make a big difference as I expect the quality of say a 70-200 L2.8 IS II will produce a different image than a 24-105 F/4.
By that degree, Camera to Camera comparisons can be very selective between different brands, where as at least within a brand, lens performance and difference can be mitigated.