Ok, I'm glad you said MP are not everything... BUT... when you are getting up into the 20 x 30 size, the more the better. You should be able to still get a good quality print at that size with your 14 MP camera though. You said nothing about your LENS. What are you using? You need a "professional" LENS as much, if not more, than a "pro" body. You need a lens that delivers excellent color and sharpness with little to no color fringing or weird artifacts. The Canon "L" lenses are typically very high quality, but costly, though all manufacturers have lenses that are better than the entry level stuff. You need to shoot at a low ISO, no higher than 200 if you can help it. Noise, (which in reality is just electronic gain), will make itself very apparent at large print sizes. So that means you may need a tripod to avoid blur due to a slow shutter speed. What format are you shooting? You need to shoot RAW and use a GOOD RAW converter such as Capture One or Lightroom. All these things need to come together if you want a quality large print.
You mention the printer itself. Do you have any idea of how massively expensive a large format printer like that costs? You are FAR FAR better off to have your prints made by a pro lab. Mpix is a good choice, though there are many others. You could have a house full of large prints made and still not spend the money you would spend on a large format printer of your own, not even counting the ink costs.
If you just have to have a camera recommendation, I have been quite happy with my Canon 5DSr. It is a full frame 50 megapixel body and I only use L lenses with it.