Const. Raphael Bergeron said the man was sitting a table at the Montreal Casino at around 4:30 a.m. ET, when he "lost control of himself."
Police say the man threw something at security staff as they moved in.
When police arrived, the man was in the custody of casino security, but was still highly agitated.
"We had to neutralize him with the [stun] gun," Bergeron said.
The man was taken to hospital as a preventive measure.
Bergeron said it's still not clear why the man became aggressive.
Police expect to lay mischief and assault with a weapon charges.