The effort of ensuring that the US border crossing has a FAX of your vehicle "Certififcate of Title" for a used vehicle (as opposed to a "Certificate of Origin" for a new vehicle) can not be understated.
You WILL have difficulty obtaining confirmation of the FAX at the border as you cannot talk directly with an officer except for a call back service which will take anywhere between 4 to 24 hrs. If the US Border agent can not find your paperwork when you show up at the border you will be stuck for another 72 hours minimum until they actually have it. Make sure when you contact them prior to arriving and when they say they have your CofT ask for the officers badge number and name and take note of the time.
There is also an E-Mail address for some of the border crossings that can be used as an alternative to the FAX. Much simpler, just scan the CofT and e-mail again with confirmation. You can PM me for the address of the Lewiston Bridge in NY state if you are using this crossing as they dont have this e-mail listed on their website nor canned phone message.
Railton