We matched that to:

Can I open a U.S. dollar TD Easy Trade account and trade in U.S. dollars?

With a TD Easy Trade account you can trade in both Canadian and U.S. dollars for no extra fee. In fact, when you open a TD Easy Trade account, you automatically get both Canadian and U.S. currency components for a TFSA, RRSP and Cash (or any combination of the three).

Are there fees for changing currencies? 

There will be a first-time conversion cost from Canadian currency when you move money into your U.S. dollar account. After that, there are no currency conversion costs when the currency of trade and the currency of the account are the same. For example, there is no fee to buy a U.S. stock from your U.S. account.  

If you move money from one currency to another (e.g., Canadian to U.S. dollars) including buying a U.S. dollar stock with Canadian dollars, there is a conversion cost.

You can also keep U.S. dollars in your U.S. dollar account and Canadian dollars in your Canadian dollar account without additional fees.