The bugs aren’t too bad in May up in YK, but you run the risk of being stuck because the ferry can’t run. I can’t speak for Whitehorse bugs but I understand it’s about the same.
Winter in Yellowknife is beautiful. I miss it. I don’t miss the cold or the gas bill from the Command-Start warming up my car every few hours, or the shovelling, but I miss how it looks and how it made me feel.