Sunshine just posted that they will be open for summer skiing June 20 to July 5!
"Our response, when asked what we’re doing on Canada Day.
Yep, you read that right. Thanks to nearly 1000 cm of Canada’s Best Snow landing on our Rocky Mountains slopes this ski season, we will open on June 20th for 16 days of summer skiing and riding.
Our plan is to open Strawberry Express and maybe another lift starting June 20th, and offer summer skiing until July 5th."
EDIT: Just an edit to add for those coming or hiking in Banff this summer that Sunshine's village is about 2150m and a lot of the best hiking trails in the park (like Skoki, Egypt Lakes, Yoho Valley, Rockwall and others) are at, go via, or are above that altitude so keep that in mind for planning. Time will tell what is open when, but it will be a quite late year all-in-all