I don't have any Canadian clients. Not by choice, we just haven't tried pitching much up there.
Around this time of year however, I'm usually working with a client who uses a Canadian supplier.
The supplier always sends a work related e-mail on Thanksgiving. I've also had reason to attend their site on ... Presidents' Day, Columbus Day and Independence Day weekend.
Yes, we get it. They are not Canadian holidays. And probably most non Canadians don't know when Victoria Day, or your version of Thanksgiving is.
But starting a mail with "I need a quick response on this ...", and ending the mail with "Have a Happy Thanksgiving" is passive aggressively douche like.