Hi friends,
I'm about two years into bonsai and I have experience with both elms and maples, however, I recently purchased several 3 gallon junipers from a nursery this past august. As most of the stock I came across seemed to cascade or grow outward instead of upward, I was wondering what the best approach was for training junipers into informal upright style trees. I've seen everything from aggressive wiring to tying the leader to a stake and letting it grow for some time but I couldn't find anything concrete on junipers in specific. Could anyone help me to arrive at the best approach for the long term health and quality of the trunk?

I assume you have bought species that grow in a cascading / crawling fasion all by itsellf. I would recommend buying trees that grow upright by itself. Trying to get a species to grow upright requires a bit of willpower.

But yeah, you can of course put a stake next to the base and tie the trunk up and let it grow like that for some years. But I would start with a species that grows upright naturally.