I do not specifics about connecting to ConnectWise. There are several options for connecting to data sources that are not yet built into Tableau. The first option would be to export the data into a supported data source. More information on supported data sources can be found in the Tableau technical specifications linked below.
If available for the database Tableau has an ODBC connector can be used to most data sources that have an ODBC driver. I am including several resources for the ODBC connection below. There can sometimes be limitations when using the ODBC connection versus a named connection that is listed in the explicitly on the data source page.
Additionally there is data is available over HTTP, the connection to data source can be made with the WDC(Web Data Connector). I have included several resources for using the Tableau WDC below. The first link is to the Tableau Online Help on the WDC feature. Additionally, I included links to the specific section in the community and the Tableau GitHub section on the WDC.
Another option is to use the Tableau SDK, to create a .tde file of the data set to then be used in the Tableau Desktop program. Additional resources and information can be found below.
I hope these resources help!