Hi,
When I fly to Canada through LAX I have always been told to put TRANSIT in the USA address. Although the last 2 times it has been corrected to TRANSIT TO CANADA by the immigration officer.
There are always officials standing towards the front of the line making sure you have filled out the form correctly or at all, so if you are really unsure you can wait until they ask you. Make sure you take your own pen, it will save you alot of time, and make sure you get it back if you lend it to someone!
Where are you headed if you don't mind me asking? don't say Cuba!
Good luck