is it possible to create a dashboard and point the query to multiple datasources?
Two points that need to be addressed:
Dashboard with multiple queries: You can create a dashboard and include multiple widgets (which could be query response tables or visualizations built on top of these query responses). These queries can be from different data sources.
Query from multiple datasources: I am assuming you want to run join queries when you say you want to query from multiple datasources. You can do this but only when the concerned databases are running in the same machine/instance. I have tried this with MySQL. Also, you need to make sure that the user has access to both the DBs. If the datasources are hosted on different servers/are of different types, then this is not possible.