I can't say if your credit union debit card will work but mine did and my credit union is a small one from rural BC I believe it involves what networks your credit union card is tied into. If that is vague it is because I don't really understand.
It does depend how your credit union is networked, but further to that, if your card is EMV (chip) equipped (also called "SMART CARD'), your transactions will be much safer. Canada has this year joined many other countries in switching to chip technology - a move which the RCMP reports has already started to lower the rate of counterfeit transactions in Canada. So if your card is old and without a chip, change it to a chip-enhanced card before you leave. (The card still has "swipe-capability" for travel to those countries without the technology).
I walked often with a couple from Quebec who were not able to use their card in all Spanish ATM machines. On the other thread, there is some discussion that it perhaps had to do with the length of the PIN.
I am a Canadian peregrina, but based in Scotland, so my bank situation is different from yours. I have used my Scottish bank cards abroad (and in Canada) without any problem. What you need to look out for on your card are symbols that indicate that you can do transactions abroad. If your card says Maestro on it, then you should be fine for most European bank machines. What you should do is just contact your bank in Canada. They will be able to advise you about getting money out of interntional ATMs. Something that you might need to be careful about is advising your bank that you will be away so that they recognise international transactions on your credit card. My boyfriend was caught out by this while in Brazil. His credit card (to pay his hotel at a conference) was declined (quite embarassingly in front of other delegates). He managed to pay with a different card, but when he rang up the bank to ask what had happened, they said that this was part of an initiative to counter fraud and that he needed to send them a message whenever he left the country. Given that for his work he needs to be out of the country at least two times per month, he simply got a new bank.
Oh yes. This is a little off-topic, but relevant to your last comments.
I used to call my bank/credit card company before leaving for Spain and just say "Going to UK, France, Spain, Portugal for these dates', and that was ok. This year, prior to leaving, I made the same call, and was required to give exact dates for each country - arrival dates and departure dates. They say it's a new policy consistent with their new anti-counterfeit measures. No problem, but it speaks to the perils of credit/debit card use. Incidentally, a car hire firm that I used in Santiago in 2005 tried to make a charge to my credit card in 2006. Hence my own caution. A word to the wise.