Mash the highbush cranberries, then combine with water until it barely comes up to the top of the berries.
Pulse the berries until they're broken up a bit with a handblender (optional) agitating and whisking well to get as much of their essence into the water as possible, then strain. This will make a thicker pulpy coulis/loose puree.
For a clear juice, just strain them without using a handblender.
Notes
Highbush Cranberry Juice (Hot Method)This is easier (and less messy) than the cold extraction
Combine the highbush cranberries with water until it barely comes up to the top of the berries, in the kitchen we used to describe this as looking like hippopotamuses floating in water.
Bring the mixture to a simmer, then turn the heat down to low, mash the berries gently, not vigorously, since extra agitation and contact with the seed will lend bitter notes to your juice.
Cover and cook for 20 minutes on the lowest heat possible, then strain, chill and refriegerate or freeze until needed. Raw juice will last for a few days in the fridge.