I'm not so sure that Canon lost so many as you might think. I run workshops and have so far had several hundred clients. I can say that for the returning customers which are plenty that almost none has switched system, a few has bought a Sony A7 to complement the Canon. I do explain that due the DR of the Canon they need a shooting technique where they never underexpose and that is the key to get the results with the Canon sensor. I shoot Canon and Nikon side by side and do like the Nikon DR a lot, but often I like the Canon better for the colors.
We can all have our feeling about how many have changed, but I have never seen any statistics.
In the landscape-focused wilderness trips that I accompany (either as a photography tutor, medical escort or independent photographer) there have been many changes in the past seven years.
Initially, it was almost exclusively Canon bodies - mostly 5D2 and 1Ds3. It was rare to see a Nikon D700 - while this was probably a much better all-round camera, it lacked the resolution of the Canon bodies and did not have the dynamic range of later Exmor sensors.
In the following years, I would see the occasional A900 or D3x, but, by and large, it remained dominated by the Canon 5D2.
All this changed in 2012 with the release of the D800/D800e and the 5D3. I continued to see lots of 5D2s, but also saw an increasing number of D800 and D800e bodies, with relatively few 5D3s
In the trips I accompanied last year, I was now seeing mostly Nikon bodies, as well as Sony bodies with Canon lenses attached, with a few old 5D2s but very few newer Canon bodies. So the tide has completely turned in Nikon/Sony's favour.
All of this, of course, is a very narrow snapshot of one specific segment of photography (landscape) but the same seems to be reflected in the equipment lists of many prominent landscape photographers - where they used to list the 5D2, many now seem to list the D800e or D810 instead.
Re: Canon vs Nikon colours - once I take them into Photoshop it makes no difference anyway. But I find that Canon generally renders too warm and Nikon too cool.