Do you know anything about your ancestors? My guess is they come from the former Eastern European Block.
As far as I know -wicz is a Polish ending. -vich can be Russian, but it is more commonly used in Serbia and the other republics in former Yugoslavia (Croatia, Macedonia, etc.)
Also,
Stan is not an Eastern European name. Stankavich sounds more like "son of Stanko" (Stanko is short from
Stanimir,
Stanislav or any other Slavic name that starts with "stan" - to become).
Finally, I would think the original name is either Stankovich or Stankevich, but that's just an educated guess :). I would suggest swapping the "avich" for "evich" or "ovich" when researching. Also, you might consider spelling the name as Stancavich/Stancovich, but that's a long shot.
Hope that helps a bit :o)