I would like to add that at the start of the Viking Age, there was a common culture shared by the various peoples of Scandinavia. The archeological record shows us a cultural consistency between settlements in Denmark, Norway, and Sweden. Among these was Gotland, which as you said is not Sweden, but it did in the 8th century fit the common mold. From there, exiles formed the Grobin colony (in modern day Latvia), and eventually the Ladoga colony, all of which, from an archeological standpoint, can be described as Norse. These, I think, are the main evidences we have to support that the Rus were Norse.