The member countries of the European Union have agreed to honour Canadian accessible parking permits, according to a Canadian government website. For the details of the European resolution making this effective, please see the article Disabled Parking Permits in Europe.
Travel guide author Rick Steves says that permits from the USA are also honoured in Europe.
If you have a parking permit, you may as well pack it. Even if you don't plan to drive, you never know when someone might offer you a lift. That permit could come in handy.
Driving in Europe can be pleasant or horrid, just like driving in North America or Australia can.
In Europe, parking is often a big problem in crowded cities and popular tourist places. Even with the permit, you may not always get a parking place. Don't assume anything.
Even where the local authorities have provided lots of accessible parking, there are always people who abuse the system. For example, on December 6, 2006, the British Broadcasting Corporation reported that police in Scotland were clamping down on the abuse of disabled parking permits.
This sort of abuse happens in every country, unfortunately.
Bottom line: take your parking permit along, but do your homework and don't assume that driving will always be your best option for visiting some tourist sites.