I can walk and post the trot and sit to a trot. I have been working on diagonals. I have cantered a little on a lunge line before.
P.S I ride english
Ya sure your ready to canter.
But dont get frustrated with it, if you dont get it right away. Cantering requires a lot of balance and leg muscles, so I would work on getting your legs stronger, not just for cantering, but for your overall riding. and its like I said before, if you dont get it right away, dont get frustrated. It took me a couple of months before I was able to actually able to go around the arena a couple of times before breaking. Just be patient, and go with the rhythm of the horse. Its hard to get at first, but have no fear, you will get it! 
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Whether you are ready to canter doesn’t really have much to do with what you can do now (rising trot, sitting trot, etc.), but your strength and balance as a rider. Do you have strong legs and good balance? You should talk to you trainer or whoever you ride with and ask their opinion because it’s hard to judge your ability without actually being able to see you ride.
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if you have to ask on the internet if you’re ready, then chances are you’re not ready. . . go ask your trainer, i’m sure they are more knowledgeable about your skills and if your ready or not
ps you already know the answer to this question.