I'd say go for it. If you can sit the trot, then you can rock to the canter. Just don't try to sit the canter like it was a trot, or you will bounce as high as I did my first time.
Keep your knees loose and polish the saddle with your rump.
And smile. Riding with a smile goes ever so much better than with clenched teeth!
Just make sure you are on a horse who knows how to slow down when asked. Please don't ask me how I know that is a good idea...
Oh...and not everyone posts. It is a good thing to learn, but not a requirement.