In summer, Whistler becomes an alpine sightseeing and hiking destination. But there's no need to slog up the slopes of the mountain.
Take the Whistler Gondola or Blackcomb Gondola and then connect between the two with the Peak2Peak Gondola. The latter holds the record for the highest point above the ground in a gondola - 436m!
Both Whistler Gondola and Blackcomb Gondola are open from mid June to early September. At that time, the Whistler Gondola closes (the Blackcomb and Peak2Peak continue until late September).
Hiking trails provide access to various viewpoints. I've suggested 2-3 hours but honestly, you could spend all day hiking in Whistler's alpine areas! Buy your tickets online to avoid most of the (long) gondola line.