Re: cercis canadensis forest pansy
With all this heat this is a tough time to try to get a new plant established; especially in full sun. Make sure the container is well mulched. If it is possible to temporarily give it some shade (by moving the container or using shade cloth) until it gets established in its new container, I would try that. Keep in mind that in the wild Cercis canadensis typically grows in light shade.
If this tree doesn’t make it, you don’t have to give up on the idea completely but buy the replacement tree in late summer/early autumn to get it well established before being exposed to full sun in the summer heat. Also in full sun it is important to make sure the container is large enough to contain the soil needed to hold enough water for a heavily perspiring tree. (I’m pretty sure the high line trees are not in containers- I can’t remember if any of the plants up there are in containers it has been a while since I last visited…)