In Qlik Sense the ability to connect to any source depends on two things:
Does the source system have a ODBC /OLE DB driver so you can create a direct connection from the Sense computer to the data source?
Does the source system have an API you can call from a QVX or using the different Qlik Sense APIs?
If the answer to either of those is "yes" then we can read from that datasource.
In regards to SSAS, there is no native connector at least for the time being and I don't know which could be the best option, but there are drivers out there (Supported Data Source Types (SSAS Multidimensional))
EDIT: Found that in the QlikView forums, that could be reused here: Connecting Qlikview to SSAS cube
I would recommend you consider going after the source data for the cubes. Cubes typically have preaggerated data in them which will limited the flexibility of your Qlik Sense app.
Here is another discussion thread from the QlikView forum that you may find useful.