Here's food for thought; a good little article from John Vigor's blog on bilge adequacy and what might be asked of them in an emergency. Click here.
Having spoken to Officer Willoughby at Blaine Boarder Services, they would have no issues with the transportation of expired handheld flares (not pistol/gun types). Upon his recommendation I have contacted the Bureau of Alcohol, Tobacco, and Firearms, for clarification of the pistol type and am waiting for a response. I will post an update when I hear from ATF.