I think it's best to keep your critical infrastructure portable. It usually doesn't make financial sense to have a hot backup on another cloud service but having a plan to quickly switch it over in case of emergency is a good idea.

For example, using something like Terraform could spin up infrastructure on AWS, but in a pinch you could make your templates work for Google, Azure, etc.

That said, if your infrastructure is at all complex it can be very difficult to keep it portable.