Is it possible to play this Bach piece on a MIDI keyboardwith instrument set to cello?
Edit: I messed up the original question by confusing cello with violin.
[Answer tweaked after question update]
Possible... ermm... yes.
Sound good... unlikely.
It is possible to make midi cello & violin sound good, but it isn't really a case of 'dial in the sound on a midi keyboard & hit the right notes'
At least, you need some kind of controller structure, mapping velocity to volume isn't enough - you need to be able to map attack separately from volume, vibrato separately as intensity & speed, string 'overhang' depending on whether the next note is the same or a different string, note-glissando/slides, etc.
The standard sound set from any keyboard with 'built-in' sounds is very unlikely to be at all convincing without significant post-production.
[Opinion source: I was employed for a decade by a major multinational electronic instrument maker (name on request;) to produce such things as onboard & point-of-sale style & song demos for their products - & I'm extremely aware of the difference between what you can achieve with a month's work for a demo vs what is actually possible to simply 'play']
Listen to some of the demos on these links, possibly some of the finest solo emulations I have heard. [I own both these 'instruments' but have no affiliation to this company.]
Using a standard Midi keyboard, it is quite difficult to get sufficient controller data to truly emulate a cello/violin in realtime - though you can tweak afterwards in a sequencer. For realtime playing & post production, these days I use this system for iPhone/Pad as a further control surface - http://hexler.net/software/touchosc
*I just realised that very same Bach prelude is one of the Blakus demos... though I don't think it's as good as it could have been made, & is presented in a significantly smaller 'space' & closer-miked, it's a fair attempt at the piece.
It's possible to emulate just about any instrument using a MIDI keyboard, and a module capable of producing sampled sounds. You ask about violin, then feature a cello piece. Note wise it'll work, using a cello sound will be far better, but you'll need to emulate the vibrato on the longer notes. A lot of keyboards have a mod wheel, which can be programmed to do that.