There is a greater that 0% chance there is more than one Sensor size being tested right now within the pool of MA\PR hardware.
There is also a greater than 0% chance that these test cameras simply lock out a maximum pixel mode, IF Canon wants to keep that secret, as they wouldn't put blind faith in even well-meaning photogs will avoid tipping Canon's hand with every single upload out of possibly thousands a day. You can sign an NDA of couse, not to reveal the resolution, but you can NOT simply bet the rollout strategy on there being zero human error.
This kind of sensor has the electronics on the back, meaning the entire front is accepting photons. It could be for instance 96MP and simply down-sampled by 50%, and such down-sampling will be indistinguishable from 24MP with bigger pixels. (In other words, noise, sensitivity, dynamic range averaged across four pixels that capture nearly 100% of photons will be identical to one big pixel.)