If you have more than $100,000 (at cost) in foreign you are required to declare the assets on your T1 Canadian personal income tax return and file a form T1135. Foreign assets include US securities held in a Canadian brokerage account. If you did not do so you are subject to penalties, which can be avoided with a Voluntary Disclosure.
"This article provides information of a general nature only. It is only current at the posting date. It is not updated and it may no longer be current. It does not provide legal advice nor can it or should it be relied upon. All tax situations are specific to their facts and will differ from the situations in the articles. If you have specific legal questions you should consult a lawyer."