Answer: I'd give the arborvitae a chance to recover on it's own. You may be surprised to find new leaves emerging from just beneath where the old leaves were attached to the stems. If this doesn't happen later this season, you can lightly prune the branches back to force new growth behind the pruning cuts. I'd wait, though. Plants like arborvitae are vigorous growers and will usually leaf out again by summer.
Best wishes with your garden!
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