Not for people who already are dual citizens. You could always be a dual citizen by birth. Example: German expats working in the US have a kid. Kid is a US citizen by virtue of being born in the US and a German citizen because of the nationality of the parents (or even just one parent). And the kid could legally have 3 passports in this case, if the parents hold different passports.

There is no such thing as EU citizenship. You are a citizen of a country which is an EU member. Each country has its own rules. The UK does expect its citizens to enter the UK on a UK passport. Of course, enforcement is a different matter - as it is with the US.

Of course there is no such thing as EU citizenship; I expect that to be understood. It was a simple way of bundling up a series of possible scenarios. There is no requirement as a UK citizen to enter the UK with a UK passport if the person in question holds another citizenship.

DEFINITELY use your EU passports to enter the EU! As EU nationals you are entering the EU as a matter of right, not privilege, and the whole procedure takes about ten seconds - they will just scan your passports and send you on your way (they're not allowed to ask you any questions). Also, most airports have separate lines for EU nationals which move a lot faster than the non-EU ones.

If, on your return, the check-in agent queries the lack of entry stamps in your Canadian passports just pull out the EU ones and say "We came in on these". Check-in agents are used to dual nationals.

This is a side note to the main topic, however: Contrary to what others have stated, "EU citizenship" does exist.

"Any person who holds the nationality of an EU country is automatically also an EU citizen. EU citizenship is additional to and does not replace national citizenship."

source: http://ec.europa.eu/justice/citizen/