You can get a Nikon D7000 with a lens for that money, I have one and find it a truly excellent camera for Astro and for traditional photography. Also, that money gets you a magnesium alloy body, not a plastic one.
There is also a Pentax with the same sensor as the D7000, if you got that I guess you could keep your lenses and sell just the body.
I prefer the Nikon over the Canon, but it comes down to personal preferences. The metering and autofocus is definitely better than the Canon, but the image results will be much the same on Canon/Nikon/Pentax etc. I prefer the layout and the one-handed operation of the Nikon, and the loadable setups etc. it feels more like something designed for people who have to use the gear every day, rather than having lots of features that can be annoying to get to, but really, it is down to personal preference, all current model DSLRs in that price range are excellent.
Ken Rockwell is a nutjob, but his thoughts sum it up for me:
http://www.kenrockwell.com/tech/nikon-vs-canon.htm
Read the first bit, where he basically says it is much of a muchness, then jump way down to the heading DSLRs (a few pages in), some of it is out of date, but it sums up why operationally I prefer Nikon for traditional photography.
More people tend to use Canon for Astro than anything else, so you will find more owners with Canons. I think that is partially because in the past there were definite advantages to the Canon gear.