taodr,
if you are canadian, you must sign up through the canadian entity. if other brokers are allowing you to sign up via a US entity, they might not be following Canadian laws or regulations. It's a long story but IB is not doing this because it wants to. In any event, rather than why it happened, if your situation isn't resolved this weekend, feel free to PM or e-mail me with details and I'll do what I can to get the appropriate people involved (it would help if you told me who, if anyone in particular, you were dealing with.
FWIW, in many ways IB is forced to do things differently than many of the other brokers because it has affiliates that are members of many overseas exchanges and thus are regulated by various international authorities. It's not as simple as it seems.