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I personally know a Canadian who has been living in the US for many years. This year he finally got his US citizenship (and yes, he applied for it willingly). So now he is dual citizen. It is very clear that he did not give up (or had to give up) his Canadian citizenship to be a US citizen. He is vocal about being a dual citizen.
 
screech339 said:
You seems to be confusing me with renunciation of US citizenship.

I'm not talking about losing US citizenship. I'm talking about the wife losing her Canadian citizenship when she became US citizen since she volunteerly became US citizen by choice. So in theory, depending on when she become US citizen, her children cannot get canadian citizen. If she had the children before becoming US citizen, then the children are canadian at time of birth since the wife is canadian at the time. If she had children after she became US citizen, it may be an issue for the children as she is not Canadian when children came along.

Screech339

The ONLY way for a person to renounce their Canadian citizenship is to formally apply to CIC, as found here http://www.cic.gc.ca/english/citizenship/renounce-how.asp.

The OP's wife never did that, so she is still Canadian, regardless of her American citizenship.
 
It is good to know. Upon further reading on the subject matter, they do not lose their own citizenship when they become US citizen however they must renounce allegiance to the other country.

Screech339