[Brightcolours]

I reckon the natural competitors of these two cameras are the A7R IV and A7 III - less so the A9 II.
Canon will surely come up with an R1 at some stage.

In any case, it's good that Sony is finally getting some serious competition at least at the high end.
Canon really needs to work on its offerings for enthusiasts though. There are no sanely priced ultra-wide and tele zoom lenses.

The A9 II performs under the R6 in data speed and specs, and the R6 rivals the 1D X III in specs. An R1 would have a chunky 1D form factor (with big button areas, integrated vertical grip, extra battery capacity).
A9 II size/weight: 128.9 x 96.4 x 77.5 mm / 678 g
EOS R6 size/weight: 138 x 97.5 x 88.4 mm / 680g

The one thing the A9 has over the A7 III: faster sensor readout of 1/160th of second (other cameras around 1/40th of a second). The 1D X III has a readout speed of 1/60th second, and the R6 probably has the same sensor. But perhaps Canon will disappoint and give a electronic 1st curtain shutter like with the RP?
No, from the specs it is clear it also has a mechanical 1st curtain shutter.
Two UHS II card slots (like the A9 II)

"Leaked" US prices:
R6 : $2499
R5: $3899

85mm f2: $599
600mm f11: $699
800mm f11: $899
100-500mm f4.5-7.1: $2699