When working standardbreds, I usually spend a lot of time teaching lateral work, like leg yeilding and bending. The graduating circle is great and leg yielding to the rail. Like mentioned the lack of bending really does pose an issue.
If you are having dificulty cantering, cantering up hill can help, though doesn't fix the issue. I've found using a pole to pop them into the canter and incorporated with a cure can help. I usually put it on the end of the corner so they have a straight line to negotiate at first.