The 5DmII is solid and you can't go wrong. I also have a 7D and it's performance is top knotch, actually better than my 5DmII (but the image quality is a little better for the 5DmII). Buy good glass...always...and learn the ins and outs of each lens like your life depends on it. Having two lenses that you can do anything with is better than 5 lenses you can barely control.
As for Nikon, the only thing I don't like about Nikon (and I do mean the only thing that doesn't have to do with software/operating systems) is that each line requires different lenses, whereas a Canon EF lens fits almost any Canon camera...film or digital. But if you get to know Nikon well and enjoy it, stay with what you use well.
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Shot with 7D and Canon 24-105L