Actually... the "average" canter stride of a horse is supposed to be 12 feet. :) At any rated show that's what the courses will be (should be) set at. I find that to be a little long for a lot of horses though.
Anyways. The main question is, what is causing his canter to be that way? Is it just fast like he's charging forward or is it more of a rushed anxious canter? Or is he just really really excited? My first hunch is that he is not truly balanced at the canter, he doesn't really know what to do with his body, so he compensates by getting faster. If that is correct, I'm going to also guess that his trot isn't perfect and balanced yet either. The best way to correct a canter is to correct the trot. (very rarely will a horse be beautifully balanced at the trot and then not know how to canter) You mentioned activating his neck and poll at the trot, make sure you're really working his hind end as well, getting it engaged while keeping him off his forehand. I love love love the fact that you are doing so much lateral work at the trot! GOOD FOR YOU! Other then lateral work, I'd also work on some longitudinal (is that the right word?) exercises as well. Lengthen down the long side and shorten down the short side of the ring, 'go' a couple steps 'woah' a couple steps, extend and collect if your horse is ready. Basically get your horse elastic enough that he is very responsive at going faster, longer, shorter, slower, etc etc. This is all at the trot, btw. Once he gets the idea down at the trot, saying 'woah' at the canter won't be that big of a deal. If he needs something to keep him focused at the canter you can also try putting out a series of poles to get his brain working.