I'd encourage you to continue to contact United and be patient. I had a similar issue in early January, and when they say the bags are in Montreal, they are likely correct. It will take longer than the normal 2-3 days due to the UA numbers and AC flights.
By the way, I now put my name and address and flight info on an 'obvious' sheet of paper inside each checked bag, in case the outer labels and/or claim tags are removed. Learned that idea from FT!