Hi Jenny,
Yes, I believe this can be done. I'm operating under the assumption that you need this data server-side, so you can use it to make decisions when constructing the landing page, although you would use the same process to access the data client-side. Basically, in Eloqua you create a data lookup that pulls the visitor fields you're looking for, and perform that on your website. Once that is complete you would use JavaScript to build the link to the landing page, passing the required data as query string values. You need to build the link using JS because by the time the visitor lookup has been performed, your page will have already rendered in the browser. You basically have two options:
1. Pull all three fields and send them all as querystring data to the landing page.
2. Pull just the email address of the visitor and pass that as querystring data to the landing page, which then uses the SOAP api to pull the visitor fields you need. (this has a potential drawback)
It's possible the REST api could also be used in step 2, I haven't had a chance to play with it. I've successfully done this with the SOAP api though.
The potential drawback of number 2 - in this scenario you're pulling visitor fields based on the email address, rather than the Eloqua cookie GUID. An email address can have several visitor profiles attached to it - my boss and I each have 2, another coworker has 7, so it wouldn't be as accurate. A resolution for this would be passing the GUID itself in the querystring and running the API on that, but I haven't worked out a way to access that with straight JavaScript (I've seen some examples using jQuery, which adds another layer to the process).
The short version is yes I think you can do what you're trying to do, it's just a matter of picking which method will work the best for you. If you would like I'd be happy to provide you with the code I'm using for either or both methods. The client-side code is straight JavaScript, the server-side code is in PHP (which could likely be re-written in other languages as necessary).
Dave