CBC:

Dorsey, the company's co-founder and CEO, says there were a number of reasons to make Canada Square's first foray outside the United States, including relationships with banking partners that made it easier to get up and running here quickly.

In light of this, it definitely makes more sense than to enter the UK (bad guess). I still think it would be the easiest market to enter in Europe though, but I don’t know how compliant the banks would be there.

Anyway, it’s pretty cool to see that the first language supported by Square other than English is French.