From the front page of GCP Load Balancing:
https://cloud.google.com/load-balancing/
Cloud Load Balancing is built on the same frontend-serving
infrastructure that powers Google. It supports 1 million+ queries per
second with consistent high performance and low latency. Traffic
enters Cloud Load Balancing through 80+ distinct global load balancing
locations, maximizing the distance traveled on Google's fast private
network backbone.
This seems to say that 1 million+ request per second is fully supported.
However, with all that said ... I wouldn't wait for "the day" before testing. See if you can't practice a suitable load. Given that this sounds like a finite event with high visibility (television), I'm sure you don't want to wait for the event only to find out something was wrong in the setup or theory. From the perspective of "is 100K request per second through a load balancer" ... the answer appears to be yes.
If you (or you asking on behalf of) a GCP consumer, Google has Technical Account Managers associated with accounts that can be brought into the planning loop ... especially if there are questions on "can we do this". One should always be cautious of sudden high volume needs of GCP resources. Again, through a Technical Account Manager, it does no harm to pre-warn Google of large resource requests. For example, if you said that you needed an extra 5000 Compute Engines, you may be constrained on what regions are available to you given a finite existing capacity. Google, just like other public cloud providers, has to schedule and balance resources in its regions. Timing is also very important. If you need a sudden burst of resources and the time that you need them happens to coincide with some event such as Black Friday (US) or Singles Day (China) special preparation may be needed.
