Few points when connecting to any DataBase from NiFi
NiFi has Generic controller service named DBCPConnectionPool which used to create connection pool to given database and processors such as ExecuteSQL or PutSql will use this controller service to obtain connection and run the given queries.
What is needed as minimum prerequisite to start with DBCPConnectionPool
1. Determine type of Database
2. Determine the JDBC URL syntax supported by Database
3. The Database client Driver which works outside of NiFi to connect to same Database needs to be placed on each NiFi nodes on given location which can be read user who is running NiFi as service
All above needs to be provided by user , if Ucanaccess 5.0.1 client Driver works outside of NiFi then it should work with DBCPConnectionPool as well, Where you are getting this message "Given file does not exist" ? Is client driver is present on NiFi hosts and configured Database Driver Location is correct ? permissions?
You mentioned There is a Cdata driver which works but that is a licensed product" , it works from where ? from NiFi:DBCPConnectionPool?