Wait, if there a load balancer in front of your servers which has a specific IP than that is the only one you need to use as A record. The load will be split by the third-party load balancer.
If you have multiple servers that accept connection and you want to do some sort of load balancer (the actual product from Cloudflare has more functionality and more logging) then @Judge’s idea works. It won’t 100% of the time and it will delay the requests since it’s round-robin on each request with a fallback and won’t keep memory of what is working. Also, no clue if it requires a specific plan and doesn’t work on free.