The Borg Queen allowed 7of9 to join the Voyager crew as a Trojan horse so she could get first hand experience with humans from a Borg perspective. The idea being that her knowledge would help the Borg ultimately assimilate mankind

That's actually just canon for the most part. The Queen revealed she let Voyager take Seven for this very reason. She wanted to better understand humanity to aid with assimilation using the experience and information Seven gathered. Later in the episode she wanted to use Seven's knowledge to create a nanoprobe virus. The Queen also gave this as the reason why Voyager was spared and always seems to go toe-to-toe against Borg armadas. I would say this is definitely canon.