I believe the question was referring to Customs Brokerages, not stock brokers. Strader-Ferris International has a virtual US address service called myUSAddress.ca. They are a customs brokerage with over 50 years of experience.
I routinely shop online with US retailers like Target, Macy's, Tire Rack and J.Crew and have them ship to my own physical US address in Ogdensburg, NY, only 40 minutes from Ottawa. I pick up my packages and declare them myself and save $$ when compared to prices in Canada. Tires, flatscreen TVs, clothes, and electronics - all significantly priced lower in the US, plus many US retailers offer free
shipping offers within the continental USA.
Compared to other such US address services, myusaddress.ca offers so much more - email notifications/SMS text notifications when packages arrive, a secure pickup service (I am not rooting thru piles of other people's packages) and I can even opt to have these guys clear my items across the border and I pick up in Prescott (saves me having to pay $6 CAD to get across that bridge - which has been under construction all summer). Another appealing aspect of this Canadian-based service is that they deal in Canadian funds. No need to have US currency.