Assuming that you don't trust your cloud provider(s) and that an attacker may gain access to your data, no, saving unencrypted data is not going to be particularly secure, even if you're only saving partial data to each provider. There's no guarantee that an attacker won't be able to guess the missing data from the data he does have (and the more you save, the more he has to work with and the easier this gets unless you're continually increasing the value of n), or that patterns in the data won't cause all of the important parts of a chunk of sensitive data to end up at a single provider.
The security is beside the fact that this mechanism is going to be slow and complicated and require all of your n providers to be up in order for you to get or put data and therefor for your app to function.
The safe way to protect data is to encrypt it using a good implementation of a known algorithm before you send it up to the cloud. It works. it's proven, and it's simple.