How fast is a canter?

Well, It's hard to say. I have been riding since I was 12 & Have rode a few pony's in my time. So, For a pony I would say : 7 - 9 Mph. For a horse : 13 - 16Mph.But It does depend on the Stamina...

well it all depends on how big the pony is because the smaller they are then the smaller their strides are.

it vaires from horse to horse. Barrel horses tend to have a very fast canter but in western and hunter under saddle the desired canter is more of a slow lope.

There is no difference, the only difference is the hoof beats. So it is just called a canter.