I would first work on adjusting his stride in the safety of a ring. Set up two ground poles a good 6 or 7 strides apart. Then practice cantering over them getting 6 strides, then 7, then 6, etc. Really play with the throttle so to speak. If you can't get him listening to in the ring, I wouldn't even bother trying open spaces. Once you have his attention in the ring, if you have the opportunity to repeat the same exercise in an open field with poles, all the better. Otherwise, just go out and ask for the different stride lengths the exact same way you did it in the arena.
I don't know much about EQ, but if you want to do eventing, you need to be able to adjust your horse's stride to ride both safely and effectively.
You just have to see your distance...you don't have to like it.