I just sent my stallion across the other direction and it was a nightmare of paperwork. Have talked to Federal Vets on BOTH sides of the border and this was the general consensus (although no one would say it just like this) - getting into Canada is near impossible with the red tape and paperwork, etc (or if not near impossible VERY hard LOL) getting into the US is a cake walk.
My take on things is that Canada does not have CEM and does not want it so they are being extra vigilent (and getting stricter all the time). The US is not NEARLY as strict. You need your International Health Cert and Coggins and that is it.
I've been told that if it is a horse that is coming from Canada to the US for a show (as this concerned me primarily) you will need all the above from a Canadian vet within the last I think it was 6 months saying that the horse has been up there and was just down in the US for a show.
I think it might also be the luck of the draw in who you get in the Canada Customs booth when you bring horses from the US into Canada
I just picked up 2 mares for breeding in Michigan last weekend and I just looked at their Export Health papers now. There is a CEM addendum with their paperwork stating that the mares havent been in FL or TX, they havent been on any premises with CEM, dont appear to have CEM, etc
When I got to Canada Customs, the official looked at the paperwork, didnt stamp anything, asked me how long I was gone for, gave everything back to me and told me to have a safe drive.
The mares dont belong to me - they belong to the breeder in MI - and I was there for less than a minute before I was sent on my way
I have found in all of my years crossing the border - both ways - that 99.9% of the US and Canadian officials dont have a flipping clue when it comes to horses crossing on a temporary or a permanent basis. If your paperwork is in order, if you appear to know what you are doing, if they can look at you and know you arent trying to pull a fast one on them and if you walk inside and tell THEM what form they need to pull from their book for you to complete (if required) they happily acknowledge that you know more than they do on the subject ...
The only time I have had an issue with either side, was last year when Canada Customs was insisting that I pay 8% pst (provincial sales tax) on a mare I had just purchased and I was insisting that I didnt have to pay it. There was 9 of them lined up on THEIR side of the desk saying I had to pay, and I was on the other side saying I didnt have to pay and citing the tariff number as proof. They finally sent me to commercial and told me to fill out my own entry (which I happily did! )
I am sure they all hear every lie, excuse, reason, etc in the book and they know when someone knows what they are talking about and when they dont and I have also found they will admit when you know more than they do on a subject
So - if you paperwork is in order, the CEM clause is filled out, you can stick to your guns as everything has been done correctly