It is possible. But, due to the variance of feature set and functionality across the cloud providers, it is hard practically. If you take a small example and let me know, I can help you through that. I would suggest you start with AWS and Azure first. Google Cloud has a very small subset of the functionality.
Changes that you will have to consider:
serverless.yml config changes due to varying attributes
- Lambda function handler signatures (not too complex)
- varying functionality not compatible (like logs etc.)
If you can create a project and share it on Github, I can help you with it. Hope that helps.