We were lagging behind the U.S. on the vaccination front but now we're receiving between 2 & 9 million doses per week so seem to be on track for a "2-dose" summer.

That said I can't see a whole new "vaccine passport" document being created from scratch and issued by August to the millions of people vaccinated, though the border could well be open both ways by then.

I imagine acceptable proof will be something like the Gov't of Ontario vaccination receipts provided after our 1st & second doses - with the 2nd dose receipt needed to be considered fully vaccinated for those vaccines that require 2 doses. That is what is currently acceptable for fully vaxed returning Canadians under the new rules announced today.

I would imagine that the US has some sort of similar documentation from the pharmacies/clinics doing the rollout there.