There is no way that the USA wants all of Canada.....it is incompatible culturally in some spots and politically it makes California look like alt-right.
Logical breakdown would be Alberta+ Saskatchewan+BC = 10 million people (let's call it Buffalo)
Ontario + Manitoba = 16 million (let's call it Laurentia)
Cede Quebec to France and build a 100 metre wall around it - you do not want Quebec (unless you take all the French speakers and hive them off to France)
The Maritimes (Newfoundland, New Brunswick, Prince Edward Island, Nova Scotia) as a single state = 2.2 million (call it Maritimes)
The Territories either remain as territories or become part of Alaska
I think there will be a hell of a fight over the indigenous people who basically say that they own all of the country and therefore they should get it back. It would be some delicate maneuvering to work that issue as they are entitled as they come and have no skills as a group.
I would say for the first 10 years that each of states would not get senators as they are too inexperienced to actually understand the workings of the USA. I would say that maybe even pairing up senators (e.g, a bordering existing state provides senate coverage for the "new" state)
So each state gets states rights, a governor and legislature just like any state and have significant education program to train the Canadians in US practice. It may even be best to have the first term or maybe even the first 10 years run by an appointed governor and cabinet - again, likely from a neighbouring state .
Financially, you'd have to take over the Canadian debt but that may well be a relatively minor deal considering the currency is falling like a stone and heavens, who will notice Canada's $1trn in amongst the $30trn or so you already have on the books.
There are some good assets to take over, pension funds are in pretty good shape and you could shut down all manner of departments in government.
Health care would be a sticking point for many, easy way out of that is to allow each of the new states to continue with their existing health care system as a state matter and then let their citizens decide. For me, if I could save $30k on my income tax but had to pay $30k for good health care (I am 68, wife is 54) I would switch in a heartbeat as our experience in Colorado and Texas is that the health care is superior, just very expensive.
Anyway, I have said several times in my newbie posts - I have been here all of 3 days - Canada is a failed state, its collapse is getting closer by the day, but it will take an economic collapse or inspired leadership on both sides of the border to make this happen.
D.