as far as strong horses go, the less you pull on them, the less they will pull on you. It is very tempting to pull when you feel a horse getting strong and it is okay to pull, but you want to make sure you are not pulling all the time because eventually the horse will get dull to the aid and it will lose its effect. With a strong horse, you can get a better result by making sharp half halts so it becomes more of a give and take and not such a wrestling match. Lastly, sometimes (but this should not be your ﬁrst solution) you may need a stronger bit on cross country if your horse does not seem to be responding to the one you are currently using. You don’t want to use a bit that’s too soft so you feel like you are constantly having to ﬁght with your horse, but you also don’t want such a strong bit that it has a negative effect.
Maybe try a new bit and make sure that you do workouts for your arms so you can build up the muscles. My horse is like that too on cross country and that's what I did and it worked.