Horse and Pony Books
ANOTHER KIND OF COWBOY
HARPER TROPHY [CANANDA] 2007
Reprinted in paperback.
SUMMARY: Teen coming of age/romance set in the world of dressage training. Alex and Cleo, two misfit teens, find salvation in their shared love of dressage, and form a growing friendship.
Easy to find. The book is still in print and can be bought new from Amazon in the UK and the USA (and presumably also Canada).