I've never been to Whitehorse, but I've been to Alaska and other rural northern regions of Canada, and I hate to say it, but as the other poster said, you are going in the heart of bug season. I am actually planning a trip up to rural NE Canada, and I'm holding off till September because of the bugs alone. Of course your probably pretty familiar with the concept of bugs since BC is pretty far north already. Are you camping or staying in a hotel? It is neat to be out and about at 2 AM in daylight though. Whitehorse is also on the route to Alaska, so I'm sure it is setup for tourists more so than other similar settlements. I like to go Kayaking when I'm in that country, but it sounds like your flying so that would make it harder unless you rent one. Whatever you decide to do, have a good time.