First off, I'm super jealous and good luck on your trip.
All three manufacturers have some mapping done for Clearwater Lake on their social maps. Garmin's is the best. Humminbird's is the worst. None are great, but it something and may give you some ideas where to start. If you're still stuck, call Alannah at Rubi's Outdoors. She has a good general feel for all the lakes in that area and should have up to date feedback from her locals. Be sure to tell her Dean from Grande Prairie sent you, and make sure you stop in at her shop as you pass through Creighton/Flin Flon on your way to the lodge.