The magnesium on the D7000 appears to be the entire rear, entire top, and at least a small section of the front:
The 7D adds magnesium to the front:
Both have magnesium alloy in their grips. Both cameras are weather sealed. Here are some of the Nikon seal points:
Either camera will do a fine job, the D7000 is probably a little better at high ISO, the 7D is probably a little better at video. Both Nikon and Canon make excellent lenses for pretty much any occasion, both have excellent flashes. The Nikon is slightly less expensive for the body.
If you want to compare prices, be sure you pick the lenses you will want from both manufacturers as well as flashes, then add the body and see who comes out cheapest.
Personally, how the camera fits in my hand, and how I like the menus and button layout means far more than some statistics, quantity of magnesium, price point, etc. I recommend you get both in your hand, play with them, and choose the one that YOU like better.
Neither one of these is going to make you a better photographer. Someone with a 7D may shoot far inferior images to someone with a D7000, or it could be the other way around. It is how the photographer interfaces with the camera with his skill and knowledge that makes the image.
Allan