Hi and welcome,
There are a few articles on the web and a few discussions on this forum about this very topic. This is one good article. http://www.standardbredhorse.com/pacecure1.htm
I have a few questions about your horse. How old is your horse? How long did it race? Is this your first horse? A lot of standardbreds that were successful at the track are confused when you ask for a canter. They can canter they were just trained not to. So, it takes a bit of encouragement.
I think the most important thing is to have that first canter, even if its sloppy be comfortable and rewarding. I would also work on flexion and building them up to it. If you get one stride of canter that's great and build from that. A lot of people sort of assume that because a standardbred can be saddled that they know how to be ridden. This is not necessarily true. I have heard of cases where standardbreds were saddled without any additional ground work and ridden without knowing the seat cues. Some trainers skip steps and don't put in the ground work to establish a solid canter on the ground and collection under saddle.