Can I change the camera even if it is a different brand?

I bought a Nikon D90 about 5 months ago on BestBuy and I purchased a one year guarantee with it in case something happens to it. My camera is now broken and when I bought the guarantee they told me that if something happens to it, they could give me a new one. The thing is, can I change it for a Canon 60D or do I have to change it for the same camera.

First, I think you need to take better care of your things, DSLR's don't break by themselves except for very rare occasions.

Anyway, it would be up to best buy whether you can get the 60D or not.

I would agree. It's apparent you broke the camera. If you purchased insurance, if that's what it is,
then yes you can exchange but for a 60D I don't know.

I agree take better care. I have cameras I've had for 10-years and they still look / work like right out of the box.

Call Best Buy. It's the only way to be sure.