As HP is located in SF, it would seem obvious to me that most of our hubbers come from the States with Canada being in 2nd place. Then it'll be a toss-up with the other big English speaking countries UK, Australia, NZ, and even India. There are quite a few people on HP, where there 2nd language is English eg. German, French and Dutch.
I must say to the two Ladies before me in the comments, that it would be a great tragedy if they where to forget that we also have on HP that great Canadian Legend from Lake Erie, the one and only Mr.C. -- AKA "Epigramman"