I am flying first class from HND to ORD and I have a connecting flight to Toronto (Terminal 2) 6 hours later.
Is it possible for me to use a first class lounge in ORD if one exists?
There is no F lounge in ORD. Assuming your flight to Toronto is on Star Alliance, your lounge access will be based on class and status you have for the departing flight. If you are on a UA flight, that will be under the same rules as domestic US, so you would need a non UA *G status irrespective of class booked for any lounge access. if you are on AC I am not entirely sure. Either way, you will not have access to the Polaris Lounge.