Canon never used a Sony sensor in a Canon interchangeable camera. Why they would start now? They are pretty competent making their own sensors. The R5 sensor is up there with the best.
I own an R5 and have used a7Riv (but not a1) so I can confirm that the R5 sensor is among the best. In fact it's marginally better in terms of noise control/sharpness balance, compared to the a1 if dpr studio comparison scenes are any guide.
But a jump from 20fps (R5) to 30fps (R3) will require not only a faster processor, but also faster readout, to eliminate rolling shutter, particularly as the R3 is an all out sports wildlife photojournalism camera (according to Canon).
Now maybe, just maybe, Canon has had a leap in tech and manufacturing ability that will enable them to produce a sensor that is on par or better than the a1 sensor, in terms of noise control, sharpness, readout speed and dynamic range. IF that's the case I'll be extremely happy, as no one wants Sony to have a monopoly (not even Sony themselves, as they know that competition is what drives product improvement). But equally, IF Canon don't yet have that ability, or if it proves too expensive to do it in house, they may well decide to deal with Sony. Canon have stated several times in interviews that they are willing to use other company's sensors if they are more suitable for specific products.