I'll say, I've only really done multi-cloud for cases where I liked different products on different clouds -- the main app and data on AWS, but using Google's data stack (BigQuery >> Redshift imho).
In terms of reliability, I think the first step is multi-region -- being able to failover to another region should your primary region have major failage. But assuming you can do that, doing multi-cloud for the same thing shouldn't be so hard provided you have some sort of common open source runtime to run on both platforms.
In terms of reliability, I think the first step is multi-region -- being able to failover to another region should your primary region have major failage. But assuming you can do that, doing multi-cloud for the same thing shouldn't be so hard provided you have some sort of common open source runtime to run on both platforms.