Air carrier First Officer reported a near mid air conflict with another aircraft that was not communicating with ATC. ATC altered their vectors to final and the First Officer disconnected the autopilot and took evasive action.

Narrative

I was PF of Aircraft X ZZZ-MKE. We were performing the visual approach to 7R at MKE. We were using the ILS 7R for situational awareness. While we were on base; ATC informed us of an aircraft that was near the approach course that they were not in communication with; so ATC altered our vector to final slightly. Eventually; we joined the final approach course. We had the aircraft in sight. Just a couple miles from the FAF; FIDNO; we realized the aircraft was approaching our direction of travel; approximately 300 feet above our approach course. We were at 2;700 feet. Within moments of realizing that; we received a TCAS RA to 'monitor vertical speed.' I do not recall receiving a TCAS TA prior. As PF; I disconnected the autopilot and followed the command. We observed the aircraft pass directly over our aircraft by 300 feet; according to the TCAS. We were clear of conflict right around the FAF. The CA/PM reported the conflict to ATC. We continued the approach to landing normally.Cause: We had the conflicting aircraft in sight prior to the traffic conflict. However; it was difficult to determine its direction of travel.ATC also was not communicating with this VFR aircraft; so it was hard to know what its intentions were.