As a Canadian (Tdot).. I know it can be relatively difficult to get a job down here in SF. I was lucky enough to go to a US school which gets me OPT for a year. Then I can issue myself a TN-1 or H1B.
I'm a Canadian who has worked in the US a number of times as an intern. J-1 visas were easy to get for me through my University career office and employer working together.
I know plenty of bay-area startups hire undergraduate interns from the University of Waterloo (where I am).
I don't see it being a problem, though it's a little costly. You should contact a company like Cultural Vistas (http://www.culturalvistas.org/) who can get you the J-1 visa.
For Canadians.. try to get a TN-1!