Canadian Visa with expired US visa?

[virap]

 Hello, does anyone know if it is possible to get a Canadian tourist visa in U.S. while having an expired US visa?

I have an invitation from a large organizations stating that I will take care in a large conference. Letter from the headquarters of the same organization overseas stating I will be returning after Canada to the home country. If necessary could take the tickets back to home country from Canada with me to interview.

Thank you in advance.