Here is the good news Jenny.... EU Regulation 261 is your best friend. You are entitled to about €600 compensation. This is cash compensation. Write to Air Canada and assert your rights under this regulation. Here is the outline of your rights:
Flights which are subject to late take-off times should also become more bearable thanks to the regulation. Depending on the flight distance and length of delay airlines must provide passengers with: free meals, drinks and two phone calls, emails, telexes or faxes; and/or compensation up to €600.
3,500km + e.g. London > New York
Delay to destination, More than 4 hours:
Compensation amount €600
Any postponements of longer than 5 hours will also make passengers eligible for a refund of the ticket (if they decide not to travel), and if it continues into the night, hotel rooms, and transfer to it, must also be provided.
You can assert your rights by contacting the airline in the first instance and demanding your rights. US & Canadian carriers have in the past tried to assert that the regulation only applies to "community carriers". This is not true if the flight originated in an EU airport. Last time I checked, Dublin was in the EU. They may also attempt to say that the delay was caused by events beyond their control, such as weather or mechanical breakdown. Whilst this excuse seems to work with the lilly-livered regulatory authorities in the US & Canada, it does not work in the EU. Neither of these excuses are valid. In fact, the volcano disruption was deemed to not be "exceptional" and required the airlines to compensate passengers.
If Air Canada fail to respond adequately, file your complaint on line here. There is a link to complain directly. They will then take it up with the airline. If this fails, go to small claims court, with the evidence the Irish regulatory authority provides that they are in breach. You will win and technically, you can instruct the bailiffs to seize a 757 until it is paid. Wouldn't that be lovely!!
http://www.aviationreg.ie/
Hope that helps.