Most of the top-end sensors read out top and bottom - though some Canon sensors have the 'column' lines running along the rows. I found this shot of the R5 sensor on a Canon site

What's interesting is the very large number of bonding pads regularly placed top and bottom. Contrast with a similar pixel count FSI integrated ADC sensor (IMX094)

Notice two things. One that it has far fewer contacts top and bottom (and that they are irregularly positioned) and that they are connected directly to package lead-out pads. Those connections are absent in the R5, suggesting that the connect to something else inside the package. Notice also that the top and bottom borders on the IMX094 are larger than the side borders, in order to accommodate the ADC circuitry, whereas all the borders on the Canon chip are the same size (though much larger). I'm not saying it's a slam-dunk, but it does support the idea that canon is using a multi-chip package with the ADC chips integrated at the package level.
As I remember it was a diagonal distortion, which could go both ways.