You create only 1 portal.
Run it on DMZ interface (2x ISP IPs natted to that DMZ IP tcp/80, tcp/443 and udp/4501).
If your users are ok to add https:// manually in front of the portal to access portal address then 80 is not needed. Otherwise Palo will automatically redirect 80 to 443.
Set up 2 A records pointing to 2 different ISP IPs (so DNS resolution gives back 2 IPs for same portal).
Agent picks one of those IPs randomly to connect to portal.
For gateways you set up 2 separate DNS records
vpn-isp1.company.com
vpn-isp2.company.com
Run gateway on same DMZ portal natting public IPs to DMZ IP.
Portal config hands out 2 gateways to agents.
Agents perform latency test and connect through ISP that is closer by.
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