I am facing almost the same problem.
I was on a student visa back in the US and for 1 semester i was full time punctual student. But some of my friend from my home country wanted to come to Canada and asked me to join them. I came with them even though i didnt know a lot about the consequences of what i was doing.
We all made the refugee claim at the Canadian port of entry and they seized our passports and other documents.
Now that i am here, i learnt a lot about what Refugee claim is and what a big mistake i did.
I wanted to go back to US, to do that I asked Canadian Immigration Office to hand me over my passport and other documents but they denied, telling me that "we would give you, your passport only if you withdraw your claim."
now i have two questions that no lawyer yet was able to answer.
What if i get a new passport from my home country embassy and apply for new US visa?
and Will the US embassy issue me new visa?