I also want to do the following 3-4 days backbacking trips this year that are not very far from Vancouver, I prefer going early in the season, maybe even mid-June . it will require backcountry skills including proficiency on snow-covered trails and route-finding. I will post more detailed info soon.
Info quoted from book "Classic Hikes of North America: 25 Breathtaking Treks in the United States and Canada"
Season
Given the likelihood of bad weather, the Long Range Traverse must be considered an alpine route, even though it’s highest point is under 3,000 feet. For that reason, summer is the time to come here, but it’s a longer season than other alpine areas. Mid May to mid September is considered prime time, but most hikers come in July or August. The advantage of off season travel is fewer bugs, the downside is the greater potential for bad weather.