This answer meets the requirement of configuring one connection as Active for both ingress and egress traffic, and enabling automatic failover to the passive connection in case of failure. The reason is:
The advertised route priority is a value that Cloud Router uses to set the route priority when advertising routes to your on-premises router. The lower the value, the higher the priority1. By setting the advertised route priority as 200 for the active connection, you ensure that it has a higher priority than the passive connection, which has the default value of 1001. This way, your on-premises router will prefer the routes from the active connection over the passive one for ingress traffic.
The MED (Multi-Exit Discriminator) is a value that your on-premises router uses to indicate its preference for receiving traffic from Cloud Router. The lower the value, the higher the preference2. By advertising a lower MED on the active connection from your on-premises router, you ensure that Cloud Router will prefer sending traffic to the active connection over the passive one for egress traffic.
If the active connection fails, Cloud Router will stop receiving routes from it and will start using the routes from the passive connection for egress traffic. Similarly, your on-premises router will stop receiving routes with priority 200 from the active connection and will start using the routes with priority 100 from the passive connection for ingress traffic. This achieves automatic failover without any manual intervention.
Option A is incorrect because setting the advertised route priority > 10,200 on the active connection would deprioritize it globally in your VPC network, which is not what you want1. Option B is incorrect because advertising a lower MED on the passive connection would make Cloud Router prefer sending traffic to it over the active one, which is not what you want2. Option D is incorrect because setting the advertised route priority as 200 for both connections would make them equally preferred by your on-premises router, which is not what you want1.
Reference:
Update the base route priority | Cloud Router | Google Cloud
Configuring BGP sessions | Cloud Router | Google Cloud