If Trump is not in earnest as to annexing some part of Canada to the United States then he ought to be, and if he is in earnest then the time is now and the way is Alberta.
Canada always was an accident of history and a historical mistake; it's a make-believe country; it's been underwritten by first Britain and later America and would never have stood on its own; it always was antidemocratic and anymore it's satanic; and after Trudeau I and Trudeau II Canada never was so wrecked in a century and a half since Confederation than it is just now. In the grandest scheme, if British North America will not be British then ultimately it can only be American. Pere Trudeau half a century ago banished Britishness from Canada, then more recently Junior Trudeau abolished whatever it was his father had made of Canada, so that by now there's nothing left hanging it all together. And the only hope for the people of Canada is its disintegration, and their integration into America. The only way is out.
Not Quebec. Never Quebec. New France must never be permitted admission to the United States; it is antithetical to America, and anyhow the prospect of any generation of Frenchmen affirmatively voting for U.S. statehood is blessedly unthinkable. It may be also that Ontario would be loath to join America, being as they are "Canada" proper, namely the Tories who lost the argument and the war in the American Revolution, then appropriated the leftover imperial possessions for their pathetic counter to the American project. Ontario and Quebec before 1867 formed the Province of Upper and Lower Canada, and they might conceivably be reconstituted into that Rump Canada.
The 51st state can only be Alberta. It's the low-hanging fruit, begging pardon for the cliche. Alberta is effectively an American state trapped in a Canadian purgatory, and the cash-cow milked by Ottawa: Alberta might be expected to vote for secession from Canada and accession to the United States, in which case it might be absorbed into America very neatly. At which point the precedent would be established, and Canada may well go broke and fly apart. And thereafter the United States would be in position to pick off the debris, in the West and the Maritimes.
As to the three provinces of the Maritimes and the two Prairie provinces east of Alberta, it may be that their populations and economies are too insignificant to warrant admission to the United States as states unto themselves. But the Maritime provinces were at one time all of them Nova Scotia, and they might be consolidated into a unitary U.S. state, called maybe The Maritimes, with the three constituent provinces of Nova Scotia and New Brunswick and Prince Edward Island being retained as regions. New Brunswick shares a long border with the United States, then Nova Scotia is connected contiguously by the isthmus, and PEI today is joined to the mainland by bridge. The new state capital could only be Halifax, which might make also a major American port on the North Atlantic and Arctic trade routes and a major American naval base, the ideal harbor jutting out well into the North Atlantic.
The Prairie provinces of Manitoba and Saskatchewan are vast territories with modest populations of something over a million each, and for that same reason of population and economy they also may want consolidating into a unitary state of two regions for admission to the United States, called maybe The Prairies or "Manewan". British Columbia may be another matter, for reasons of size and of politics, but in the event that Alberta joined the Union, BC would be enveloped on three sides by the United States, and already half its coast is Alaskan, then in the event that Saskatchewan and Manitoba followed Alberta into the Greater United States, BC would be far removed from Rump Canada.
Yukon which borders Alaska and the whole or part of the Northwest Territories and Nunavut might be annexed and administered as territories of the United States, called maybe the United States Arctic Territories or USAT (you-sat). As to Newfoundland and Labrador, Labrador which is a northern extension of Quebec and Newfoundland which is quite independent of the Maritimes, and the whole of which may be too tiny in the way of population and economy to warrant admission to the United States as a state unto itself, I've not yet decided what's to be done with them.