I know that if one has a duplicate/overlapping booking on the same airline, 99% it will get cancelled (e.g. a booking for both 8am and 10am SFO-JFK flight on the same airline).

But what about two different airlines (specifically in my case, United & Alaska).

Do their backend systems talk to each other?

For reasons, I need to book both SFO - SEA (on Alaska) and SFO - PDX (on United) at the overlapping same time, and wouldn't know which one to take till the day-of. I will not attach my mileage numbers etc.

Are there any data points on cancellations in this case of the overlapping flight?