That should be fine, you can enter the US on that visa so being in transit should be fine.
Your passport (with PR visa I assume as you have a US visa you likely aren't visa exempt for Canada) and COPR is all you need to land. And a bank statement.
I found this: http://canberra.usembassy.gov/transit-visa.html
The main advantage of the B-1/B-2 visitor visa over the C-1 transit visa is that the B-1/B-2 visa can be used for visits as well as transits through the U.S. during its period of validity.
The offiical US page is here: https://travel.state.gov/content/visas/en/other/transit.html which indicates you should be fine.
Proof of your onward travel arrangements and/or permission to enter another country after departing the United States may be sufficient evidence that your purpose for entering the United States is transit.
Having a onward ticket for Canada with a COPR should be more than sufficient
Which airport in the US are you going through btw? Some are better than others, avoid Miami for example but the likes of EWR and ORD are continually ports of entry to and from Canada. I once flew Toronto to Newark and because our flight was late I was on a plane back to Toronto 2h later for different routing! US customs didn't care (granted I wasn't on a visa but you get the idea)
