Ive used Nikon's for decades and never been able to wear one out.
But have had other brands which did not hold up as well. The D300 is built like a tank. You need to "Handle both cameras and shoot the same thing with each camera."
Personally prefer the NIKON especially with the battery pack. With big hands other cameras seem like toys.

With small hands, you just go without the pack.
Trying to make a decision based on other people to me makes no sense. Choose a camera whose features fit your needs. If you already had Nikon lenses, the D300 can use them, where the Canon will not. If you had Canon lenses, the same would apply.
Most who give their reasons, like me will be slanted in favor of what camera they use. Few will have used both extensively, so can't advise you a choice between the two. Ive used both, had a Canon years ago, switched to Nikon and never looked back. But, today they are not like the one I had, so what Id say about it does not apply.
Generally Nikon owners realize this, so do not waste time saying "too bad you were not using a Nikon." Those who would, do not realize the BRAND of camera you use makes NO difference. It is what you know about HOW to use it that makes the difference.
In 1939 could get great pictures with a Kodak Vest Pocket Brownie. When I bought a better camera, it was only more versatile so I could get just as great pictures under more difficult situations.
Today, can create even better images, not due to a brand of camera, but because of what Ive learned in 73 years of photography. Some buy a more expensive camera thinking it will make "better" pictures. Then are disappointed because they do not know how to use it. Many times if they kept the camera they had, and spent three months intensely focusing on learning how to use it, they would be satisfied with it. Spending a year in an Adult Ed Photography class could do much more for them, than a new camera.
Go to a store which will let you shoot some digital shots on your own card. Take some with each camera of the same subject, using automatic settings as you will not be familiar with manual. Realizing you still unfamiliar with both. Take the card home and see what you like or do not like about them and make your choice.
Then, learn to use it as well as you can use your hands.