How do you get 100 drunk and rowdy Canadians out of a pool?

How do you get 100 drunk and rowdy Canadians out of a pool?
You say "Please get out of the pool."

This is a Canadian joke, which is a common type of joke in the US. The stereotypical Canadian is (according to Americans) very polite, so this joke plays on that.

It is expected that a person that hears this joke will recognize that this fulfills that stereotype, and that will be humorous. To get 100 drunk and rowdy people out of the pool would probably be difficult in real life (even if they were Canadian). That is probably the funniest part of the joke.