Most Canadians know Ukraine and Ukrainians, especially true after Russian invasion.You guys are stressing out for nothing. Sorry to disappoint you but for everybody outside ex-USSR all USSR-born are russians whether uzbek or tajik or bulgarian or armenian. They do not distinguish among us - we are all the same to them. So most people will not even notice the subtle difference.
But here is how I did it. I was born in USSR and today it is an independent country. Let us suppose it is Azerbaijan for the sake of example. So I put the name of the country of birth/citizenship as its name as of today i.e. Azerbaijan (without any SSRs). I did not declare USSR either. And on the interview I said I have this citizenship by birth hence from my birth date (note since 1991 when it got independent).
I am not arguing this is the legally perfect answer, but I did not have any problems - I got decision made and waiting for oath now.
They care about the number of your citizenships (using today's names of countries) - they are less stringent on historical details. Just declare all passports you have and bring them to your test.
I personally never was called Russian.
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I wrote in mine USSR and then Ukraine.