Trot to canter on an Icelandic horse

It sounds as though you need to practise the canter strike-offs. At the moment it seems that, at your canter signal, he loses his balance instead and so falls into tölt or runs off from you. Work on a school or in a round pen, ideally starting on the lunge. Put out a single pole. From trot, I tend to use a voice cue that I want the horse to link with the strike-off, for example "Canter!", which I ask for right over the pole from trot, combined with a driving aid from the ground. Once this works from the ground, it helps to keep someone on the ground giving the same cue while you ask for the strike-off from the saddle, over the pole.

With an Icelandic that has a strong lateral movement pattern (a lot of pace or tölt), it is important to ride only a few strides rather than letting the horse break the canter through lack of balance.

Good luck 💫