I designed a CAN/USB device for my company and we sell it via the web. In my experience, I have only ever heard of one common API that was requested by a potential customer - I can't remember what it was now and never heard of it again, so that may be a good sign that it was not widely used or adopted. Of course I never really ever looked again, so I may be completely wrong.
We ended up creating our own custom API, but really its almost as simple as Open, Close, Send, Receive. Users of the API are usually not too intimidated by such simple functionality, and there is not really much software out there (at least that I'm aware of) that uses a common driver API anyway.
I'm not familiar with Vector, but do they have an API that will allow supported hardware to work with their software? Perhaps National Instruments has something that will let users seamlessly plug-in your CAN hardware.
Let me know what you find - I would be willing to make our hardware work with it as well.
