There's a questionmark over maintenance at the moment I think (as well as lots of other things), on which there's supposed to be a court ruling about two years ago. I'm still waiting on a decision on a complaint I filed in January 2010!
I would think that some maintenance problems are just bad luck, some are the fault of the airline.
Anyway, write to Air Canada. If/when you don't get your euro, you need to file a complaint with the Irish Aviation Regulator (as the flight originated in DUB).
http://aviationreg.ie and look for the link to the complaint form on the right. Lots more info on entitlements there too.
Worst case, the Aviation Regulator rules you're not entitled to anything. Best case, it's 400 free euro.