Which Nikon and / or Canon DSLR has the most megapixel as of Jan 2013?

I have had the Canon EOS 1100d for a year now and it only has 12.1 MEgaPixels. I would like to get a new DSLR body with much more Megapixels. I will be using the camera for astrophotography so the more megapixels I have, the more bigger the image will be. This is for the future, but I'm just asking this now.

Added (1). I do own two canon lenses for a DSLR, do you think it would be wise to keep buying Canon stuff so I don't have to buy new lens for Nikon because Canon lenses are all I have. It may be more convenient since I already can use Canon lenses. The Canon lenses won't work on the Nikon right?

The Nikon D800/800E has 36.3 MP (that's on a full frame not APS-C sized sensor). Don't know about Canon.

The number of megapixels is totally irrelevant. 12 megapixels is absolutely fine for astrophotography - in fact lots of professional purpose-made astro cameras have only 1 megapixel or less.

What's more important is the low-light capability of the camera, the telescope you use, and your technique.

You can count pixels all you want, but that is not the only thing you should consider. Also look at the fact that for astro photography, you're not dealing with a lot of color, so your kind of wasting most of the camera. Also cramming all those pixels in a small space means that the sensor is going to get a lot hotter, a lot quicker. That means noisy images that will go through a lot of battery power. Frankly DSLR's are not a good choice for this type of stuff, they are best used when your subject is close and the shutter is relatively fast.

I would seriously consider using a film camera, you'll have to learn about reciprocity, but noise is greatly reduced and you'll save on all sorts of power. If you can get a medium or large format camera, you can actually make far superior images than a DSLR of any quality.

If you go top-end to get over 30 Mps you will need to change lenses also, since the Canon 1100D is a 'crop frame' camera - the cameras of any brand with 'full frame' sensors need different lenses, especially on the wide-angle end.

Indeed Canon lenses will not work on Nikon, Sony, etc, and vice versa.

Nikon D800 with 36 mega-pixel
Canon EOS 5D Mark II/Canon 1D with 21, 1 mega pixel
frankly speaking you don't have necessarily to use the most professional cameras in the DSLR market.
A canon with the half price will fit you perfectly. For example canon 60D 18 megapixel. The only + is better low light performance, otherwise the quality of the image is almost the same.
+ Read the comments above about how important is the megapixels in a camera…

About the lenses, if you want nikon lenses in your canon body you will need a lens adapter to do that.
Not suggested.

The Nikon D800 36.3 MegaPixels. There's also the D800E, which is nearly the same as the regular D800 but it is more suited for astrophotography.

The D800 is 3, 000 USD, and the D800E is 3, 300.

For Canon, there's the 5D Mark III, which has 22.3, and the 5D Mark II which has 21.1. They're priced at 3, 000 and 2, 000 respectively. Cheaper alternatives are the Canon 7D, and Canon 6D, which are both around 1, 000 USD.