Too broad a question with no real answer....but I agree with Danny's comments (and calculations).  I think it would be best to give us a bit  more information regarding your budget, your image sales plans and an idea of what you will primarily be shooting.

The reason I say that is...with the few criteria you have given us, the DSLR suited for the task will cost you $3000+US for the body alone.  Add to that $1000+US for each lens, $500US for a flash, plus cards, bag, tripod, etc....

I'd hate to recommend that type of expenditure for someone new to DSLR's.

What I will add, in addition to what Danny has said;

1)Canon 5D is a better choice than the Nikon D2X

2)If you want a better "out of the camera" shot...one that requires less postprocessing...choose Canon over Nikon

3)As printed image sizes increase, the viewing distance also typically increases....so, you can drop the required dpi somewhat...but I agree with the 300dpi for A3 high quality

4)High quality glass generally equates with a high quality image( I don't mean composition!)....High quality glass generally equates with high price....Glass will not depreciate in value as fast as your camera body

NOTE: I'm sure points 1 and 2 may cause some folks to spit out their morning coffee....(Go ahead argue all you want....just my opinion and I'm not even a Canon guy!)  Take a look at the quality of Danny's 5D images...they speak for themselves.

Anyway, give the folks here some more criteria...then they'll be in a better position to help you narrow things down.

In youth, we learn....with age, we understand.