I don't agree that the lungeing is SOOO important. I have two otstndbds now. I have had two others. All learned to canter with me in the saddle, except the newest one ( a trotter) who is still in serious training.
I don't lunge for various reasons. What I did do was watch them in the paddock -- when did they canter on their own? When did they pace? When does the trotter trot? I saw that where the ground is even and predictable, they would pace; where the ground was rough they would canter. So, when I started training them under saddle I asked for a canter on rough ground.
Anytime I asked for more speed on the gravel road I live on, or in the even field I have, I would get a pace... but now, I can get a canter all the time from my girl! Also, The bending does help a lot... it seems to be extremely difficult, if not impossible to complete a defined turn in a pace, so ask for lots of corners. The trotter -- well, that's a whole other story...