It's simply not true. Just read the book "The Continuation War: An Investigation of German-Finnish Military Collaboration 1940-1941" by Mauno Jokipii (there is a Russian translation of this book). Finland joined Germany before the Soviets attacked - German bombers began mining the Gulf of Finland, taking off from Finnish airfields a few hours before the Germans attack on the USSR.Just to say that Finland joined Germany in attacking the USSR after the USSR attacked Finland in June 1941. Moscow had a choice, Helsinki did not.