Making it in the LA film industry as a Canadian?

I am a 23 year old Canadian trying to begin a career in the film
industry. As far as I have read about beginning a career in the film
industry is that production assistant jobs are the way to start. (I
have worked as an extra on many films/tv as well as Interned in
television production for 8 months) Those jobs however are proving to
be few and far between in Toronto. I would love to take a risk and
move to LA to really get my hands dirty, but I wonder what the success
rate is of a Canadian relocating to Los Angeles for work. Is a work
VISA difficult to acquire? Will production companies hire Canadians if
there are US citizens capable for the job? How long can one live in a
US city as a Canadian? Being from suburban Ontario it is hard to get
answers to these questions because most people just arent interesting
in this kind of career! Any input or advise would be greatly
appreciated!