[davidmanze]

https://www.canon.com.au/about-canon/news-and-press-releases/more-details-of-eos-r3-revealed

     Interestingly, there're holding out on revealing the resolution of the sensor as if it's not a key specification ........ I was thinking it would be 20 Mps using global shutter technology as BC had alluded to some time back ..... other sources were alluding to it also ........ in which case why state:

"flash sync is now possible with the electronic shutter when used with external speed-lites and rolling shutter for fast moving subjects has been reduced"

........ the key word being "reduced" ....... rather than eliminated !!

.... is it using electronic shutter/ global shutter or both ??

I don't really remember typing about it having a global shutter... I remember Canon announced a month ago it will do 30 FPS with full DPAF and AE, and the sensor being a stacked. back side illuminated sensor. 
And that it will have a faster read out to limit rolling shutter.

A "global shutter" is an electronic shutter, by the way.

    I understand that ...... it reads all the pixels at once ....... as opposed to scanning in this case at high speed à là Sony A1...... 

here but in reference to the R1:

"Another sensor, this time in rumour space, is a 21mp FF sensor, with global shutter. It is suggested to be for an "EOS R1". 120dB dynamic range, 120 FPS full readout capable."