can we vary the content that it shown based on the target it sees through the cloud
Sure you can; the targets (Image Targets) which are stored on the Cloud define a set of images that can be recognized and for which Vuforia can compute a pose; you can then "augment" each target with the content that you like (e.g. 3D models, textures, videos, ) etc.
The content that you apply to a target is completely handled on the client side (i.e. in your App running on the device), it is not stored on the Cloud; however, with each target on the cloud you can also store some metadata (which you can retrieve together with the target itself when the target is recognized); the metadata can be any text, and you can use such text information to decide at run-time what content you want to load/use for that specific Target.
Another option is to retrieve the unique target ID of the recognized target and based on such ID, decide what content you want to display for that target.
Essentially, you can think of the Cloud like a huge database that you can access via the net, as opposed to a local Device Database which is stored on your device and can only contain few tens of targets (100 at most).
I hope this answers your question.