A Standardbred that has been raced, or brought up to racing fitness, does not have the same muscles built up that a riding horse does. Because of this, your horse will be more inflexible to round his/her back up, which helps smooth out the trot.
Contrary to popular belief, pacers DO know how to trot, and often shuffle back and forth between them while being jogged, if they are without hobbles. Just like they DO know how to canter, they just have been taught to not when working.
If you have gotten a pacer, rather then a trotter, it will most likely take more time and energy to train him that you would prefer that he would trot then pace...since when he was in training, he was told he was to pace, not trot. This will take some skill on your part, as you will have to correct it within a few steps, and be able to tell the difference from a trot and a pace under saddle.
Your horse will not have a very good canter, until he is more balanced under saddle. You will need to do a lot of trot work, a lot of bending. When you get there, you might have a hard time encouraging him to stay in the canter, so make sure that you are the one who decides to start and stop cantering, not him.
Your horse isn't lazy, it is just that he was taught differently.
Not sure where you are from, but the Ontario Standardbred Adoption Society normally has some literature on retraining.