A Parks Canada staff member has written on the "Jasper Trail Alliance" facebook page that the Cavell Meadows trail will be closed until July 15 to give the meadows a chance to dry out. (Posted on June 26, under "recent posts by others".)
This is about two weeks later than the usual time when the trail opens, and is due to the huge amounts of snowfall we had last winter, and the cool, rainy spring and early summer we have had since.
This is unfortunate for those visiting before that time who want to hike the trail, but is absolutely necessary to protect the fragile subalpine ecosystem up there. When the meadows are wet and/or snowy, people wander off the trail to avoid those spots. With such a short growing season at that elevation, the trampled vegetation doesn't have a chance to recover. Over time, this creates braided, erosion-prone trails. Because it is such a high-use area, it can be literally "loved to death" if not protected from overuse when vulnerable.