Improving canter strike-offs

I've got a pony I ride about once a week. He's nearly always struggled with the canter, so I'd love any tips for improving it. I can get a good trot and put my canter leg on, but he still doesn't strike off. It usually ends with me totally out of breath and giving him a jump because I get so tired after trying loads of times :/ Any tips gratefully received 🙏🏻