In Dec 2017, I completed my trip from the US to Canada, without PR card, and just COPR and Passport. Also, as mentioned earlier in this thread, I did not have my own car. Here is my experience.
I was based in Pittsburg in the US. So, I flew to the nearest border town, i.e. Buffalo, from Buffalo airport there are multiple options. You can rent a car, take a greyhound to the border and then walk over as some members suggested, or there are tons of taxi services.
I opted for a Taxi service from Buffalo Airport to Downtown Toronto. The ride cost me $250 US, it was less than 3 hr long. At the Border I showed my passport and COPR, the oficial asked me where I would be living and how much cash I am carrying. That's it, less than a minute at the crossing, I did not even step out of the car. Thereafter, it was straight to Toronto.
I hope this information is useful to others in a similar situation.
Regards,
DV