GV will not allow you to spoof a caller ID. If you want to pass the original caller ID on a bridged call, the outbound leg must use a provider that permits spoofing. Unfortunately, I'm not aware of any free ones. Anveo is a good choice; calls to most of Canada are $0.005/min, with 30/6 billing.
Alternatively, you could get a US DID from a commercial provider that forwards to your Canada number (this has nothing to do with the OBi). In theory, VoxOx should be a free solution, but AFAIK there is no way to make it pass DTMF, so you would be unable to verify the number with GV.
You could use a free Callcentric (New York) DID, which you could forward via iNum to VoxOx, which would in turn forward to your Canada number. Though this would be free, I wouldn't expect a chain of three providers to be reliable or have the best quality. Also, you would have to state that you were using CC outside of North America, to avoid the $1.50/mo. 911 fee.