I'd go with the Nikon any day. I used to own a Canon 40D and frankly I wasn't very happy with it. Or rather with one aspect of it... the pictures. I shoot a lot in low light, so I tend to use higher iso-s. And anything above iso 800 was not usable for my taste. Lots of chroma noise with visible banding. If you use Lightroom and shoot in raw its easy to correct, but frankly I don't post process every picture I take. Apart from that it was a superb camera.
If i may ask, how much did you find the D300 for? I was looking at the D300s
. But it was around 40% more expensive than the D7000. So I went with the latter.
I went with Nikon for a variety of reasons though. The most important being the image quality. I just like how nikon handles noise, it has a more grain like appearance compared to canons's blotchy squares. Some people don't mind that though. So you really have to make up your own mind.
Close second is the fact that my sister "borrowed" my 40D shortly after I got it and never gave it back. Since she went on to study digital media with a focus on photography because of that, it didn't feel right to demand it back
thus i went with nikon so she couldn't "borrow" any more gear from me.
I did prefer the ergonomics of the Canon a bit more though. But thats comparing the D7000, not the D300.
I would suggest you try out how each feels in your hands as well.
Hope I didn't confuse you even more. I remember how I felt when I was buying my first dslr.