Pete offers excellent advice that would apply on pretty much any river.

As a former river manager and guide training director, I've always looked at personality, work ethic, and people skills as higher priority than initial river skills.  Many an experienced kayaker has washed out of guide training due to attitude.  Many a great guide has started out not knowing an eddy from a hole.  You can teach the mechanics of whitewater far easier than you can change someone's attitude or ability to work with people.

If you come across as someone who wants to help any way you can and is eager to learn, you'll be in good shape.

It's also good to start now lining up your options.  Talk to the companies you're considering, and any friends you may have who work for them.  Figure out which is the best match for you, then go through their application process and periodically check in to check your status and let them know you're still excited about working for them.

Remember that across the industry, numbers are dropping.  There are more wannabe raft guides than there are positions available.  Managers can be picky about who they take on.  That doesn't mean there isn't work to be had, but reinforces the need to have an "I'll try harder" attitude before, during and after training.  Seasoned guides are critical to any staff, but new energy has a lot of value as well.

Good luck to you!