You did not answer the question: do you have specific sales numbers for Nikon D800/E and 5D III?
My personal guess is, that Nikon sold more D800/E.
If you had followed the sales trend for the D800 vs 5D3 on US Amazon charts, you'll notice D800 took the lead initially with 5D3 trailing just slightly behind. Now, the 5D3 is in the top 10 while the D800 is nowhere positioned in the top 30 DSLR. Give it another year. If you see the same pattern emerging in mid-2014, you can be quite certain the 5D3 has completely trounced the D800 in sales.
In case you wanna argue it's all about pricing, I can assure you that's not the important factor at play. Rather it's the poor factory QC that killed the D800 sales. Check out the customer reviews: (i) for 5D3 - out of 327 reviews, 278 were 5-stars and 31 were 4-stars (ii) for D800 - out of 309 reviews, 189 were 5-stars and 26 were 4-stars. Pretty big difference there. Remember the left side focus problems with a number of copies of the D800? That's just one example.
You'll see similar sales trends for 6D vs D600 (remember the Nikon factory debris issue), 5D2 vs D700 (well it's 21 vs 12 MP) etc.
The single biggest advantage that Canon has over Nikon etc is the massive success they achieved during the early DSLR years. Canon had such a commanding lead with the release of their sub-$1000 DRebel 300D (despite all the fanboy attacks on its poor AF capabilities, relatively smooth high ISO performance etc) that the competition has never been able to match, not even today.