Although the 9-pin connectors look the same for CAN and serial devices, you cannot use the CAN protocol on an RS232/RS485 interface. If the Mass Flow Controller is using the CAN protocol, then you will need a CAN interface.
Below you will find a link to a site that describes CAN in detail.
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/7a542c58102774db8625680700606293?OpenDocument
Here is a link to the online catalog showing a CAN interface.
http://sine.ni.com/apps/we/nioc.vp?lang=US&pc=mn&cid=1335
Kim L.
Applications Engineer
National Instruments