778-771-4102
You will receive a robotic message thanking you for calling the CRA Collections Help Desk (is that even a thing?) and then you are told to please stay on th eline to be connected to the next officer. Phone usually rings about 3 times, the message plays again and often the scammer picks up and is ready to go. I will say that I have angered them quite a bit as I literally got a hold of the same guy 12 consecutive times and blasted him with the "Ha Ha" sound effect. The sighs, groans, and obscenity-laced tirades almost make this silly little hobby worthwhile. :)
BTW- I don't think a Canadian number is necessary... but I could be wrong.