Based on experience coming in at Coutts, bringing horses back into Canada with previous paperwork in May 2010 and again in August, a Canadian Border Vet checked the horses and there was a fee. I got to the border at 3:50PM and paid over time to 4:30PM.
On the same two trips ( May & Aug) we had one horse per trip that we'd just purchased, the same Canadian Vet inspection was required for each of the new horses coming into Canada.
I am not an expert, I base this info on my experiences in the last 5 years of taking horses across the border.
Perhaps there are some short cuts that I am not aware of, I'd welcome additional info from anyone with the expertise.