I don't think that they will implement that type of a requirement. If they do...it not only would make many Canadians ineligible, but it would make many from the European countries unable to travel into the US. They will NEED our travel dollars. Many countries have mixed dosing, because of availability.
Once the CDC updates their findings/testing/researching (which they heavily follow recommentations of the WHO) there is a very high probability that they will follow the same guidelines as what the WHO that state the mixed doses are considered " fully vaccinated".
It will be interesting to see how this plays out. Honestly, at this rate of the boarder opening, many of us are going to be needing our " booster" and that will be what our second dose was. I can't help by shake my head at everything thing at this point