High Availability and Load Balancing for Single-Node CE with multiple ISP uplinks

You can also deploy 3 standalone CE for each ISP and group them in a virtual site. 

For 3 CE cluster max 2 RE connections will be available as this suggests 2 ISP can be utlized in a cluster deployment.

See my article for ideas:

https://community.f5.com/kb/communityarticles/xc-distributed-cloud-and-how-to-keep-the-source-ip-from-changing-with-customer-e/343722

If you want just single CE that will prioritize best link to be hones this seems like a job for SD-WAN siting infrount the CE system not F5 CE.