Paul, I had never thought about the "national holiday in summer" thing but when you mention it: The Swedish national holiday is on June 6 . Not that anyone cares to celebrate it. It's not even a holiday (sic!)
Canada has labour day in September??? How about other countries? I thought may 1 was universal.
Clearly, Swedes are a bit more optimistic than Canadians. The start of summer is on April 30, no matter how cold it is.