He's always had a fair amount of room to turn when he raced and even when he was being turned out after his racing career. Avoid small circles and turns because they are difficult for him. People stress "ride deep into your corners". That is VERY difficult for an unbalanced horse! Also, a standardbred ALWAYS exercises "on the right rein". The only time they are turned to the "left rein" is when they are either racing or training, which is like doing a practice run with or without other horses. If you turn him in a semi circle (like a u-turn) he may think it's time to run! As for bending his head to the outside, you have to remember that he was never asked to bend as a racehorse. Actually they sometimes put poles along the lines (reins) to prevent the horse from bending his neck - although it's not a proper riding bend anyway. Try giving him an open rein through large circles and serpentines.
Any out of shape unbalanced horse will have a difficult time cantering, let alone one that was told that cantering is forbidden for the first 11 years of his life. Work on halt/walk/trot transitions within and between gaits. Trot 5 steps, walk 5, trot 5, walk 4, halt, trot 4, walk 4, etc. This will help him find his balance, give him strength in his hind end, and allow him to round his back. At any time he breaks into a canter, praise him, ride it, and don't work against it. He has to learn that it's alright to canter. It won't be a smooth, collected, round canter for a looooooong time! It's the same as if you took an experienced hunter horse that had been off for a long time... you'd have to do a lot of w/t/c transitions, bending, suppling, balancing, etc. before he could have a correct, comfortable canter. When he raced he had an overcheck bit in his mouth which he was supposed to lean on and hollow out his back in order to run faster. He has to learn to round his back now and balance himself instead of relying on the bit. The thing is with Stbs is that sometimes they have to learn the canter too! You really need a lot of patience for this - but thankfully standardbreds are patient, kind horses.
I absolutely love Stbs. They are intelligent horses who are very forgiving. They are often bred with a longer back which is a bit of a disadvantage for cantering (or an advantage if you want them to do well in their racing careers!)
Now I have a few questions for you. What do you mean he doesn't to trot pole properly? Is he jumping them? Running out? Stopping? Does he know how to lunge properly? Do you have a kind hand?