or the 100-400 canon. I think its an f4.
It's an f5.6, which is both good and bad. The good is that, being an f5.6, it costs around $1500. The bad is that f5.6 is slow, and I don't believe that the coatings are as good as those found on the pricier lenses. If the 100-400 were an f4, it would probably cost around $6,000. That extra stop basically quadruples the price . . . and doubles the weight & size.
I think a budget-friendly option is the Canon 70-300 IS. Do not confuse this with the 75-300, which has left many, many users very disappointed. The 70-300 is a far better lens than that 75-300, and can be had for around $500 or $600. With the crop body you have it works out to be an effective focal length of 120mm - 480mm, which is a pretty decent all-around range for wildlife. It's not going to give you the same results of Canon's premium L-series lenses, but if you need to stay well under a thousand bucks it's hard to beat.
The good thing is that you really can't go wrong with Canon glass - if you buy a lens and find that it just isn't what you want, then you can always sell it used on eBay or on the Canon forum and get 70% - 85% of your money back out of it.