I am an inexperienced gaited horse owner. I have had my Missouri Fox Trotter for about 3 years and she is my first gaited horse. She was also used as a broodmare for years and I don't think she was very set in her fox trot to begin with.
She flat walks (her best gait, imo), fox trots, what I assume is a hard trot when she gets going too fast, paces, and canters. I think I have felt a rack or run walk in there too.
Anyway, as we are not showing, she is in her teens, and I am likely to be her last owner, I have decided I have a whole lot more fun with her when I just ride her and enjoy her and not worry about ruining or improving her gaitedness. I have her to have fun out on the trails. And that's what we do. We cantered just today.
She actually has kind of a crappy canter. And she paces going into and out of it. She also cross canters. But we have fun and I am just not going to worry about it. I have found that if I want to get a good, true canter out of her she does best going up hills.
I have a friend with three Fox Trotters that canter just lovely. Smooth and collected and they don't seem to cross-canter. And she never canters them on purpose, it's just occasionally they get going too fast and break into a canter when we are gaiting out on the trails. What a waste! If I had a horse that cantered that wonderful I would use it. My mare canters sucky and I still use it. For me, it's part of the fun of riding.
Now maybe if she racked instead of paced or hard trotted, I wouldn't consider the canter so important.