With a POD in 1867, change the course of history in order to make Canada a superpower by 1945. And no you can't have it be annexed by America.
Dathi THorfinnsson did a pretty good job in this regard:
https://www.alternatehistory.com/discussion/showthread.php?t=130408
Sometime before the Mexican-American war, Spain sells most of Alta California to Britain. It realises it can't defend the north long-term, and would prefer a British California to an American one.
Britain wants to keep its enormous portion of the West Coast, seeing its strategic value, but needs a clever way to keep it from America. The solution is the Confederation of Canada in 1848: British America is united into the Dominion of Canada, which consists of Lower Canada (otl Quebec), Upper Canada (otl Ontario+Prairies), Acadia (otl Maritimes), and New Canada (everywhere west of the continental divide; capital Fort Astoria), with the capital in Ottawa. The four divisions are mostly independent of one another, and New Canada sets up a homesteading grant system for prospective settlers, making any settler an automatic citizen.
Somehow the USA collapses, and many former states join Canada. This is pretty much the only way to bring Canada out of America's shadow and give it a large enough population base to be a superpower. Making the USA break up after the ACW is more or less impossible though.
What's left of the USA would still have tons more people than Canada. Plus, the POD's in 1867. You'd need an earlier POD to have the South win.The ACW drags on an eventually the people in the North decide it isn't worth to keep fighting to bring all of the dumb hicks down south back into the fold so the North quits, lets the South secede and then what is left of the USA joins Canada.
Canada has the resources, size and industry to become a Superpower. What it lacks are the people. Increased immigration would fix that, but I'm not sure how it would be managed. It's also a bit of a satellite for Britain. An earlier break from the Britiah would help too.
Britain declare war on us.
Win the war, take some land from the northern east coast. Then have it break free with Canada.
Then join the axis power with mexico, win WW2, annex more land. Done.
Obviously a good starting point would be having the Canadian trans-Pacific railway completed sometime before the 1880s and thus open up much of the better land out west in the 1870s which would have a better knock on effect for settlement and immigration (probably one of the only ways to get Canada up above a population of 10 million around the turn of the century or 1910). Making Canada more attractive to more than Anglo-Saxon immigrants earlier on is something necessary too (perhaps less of a Conservative dominated post Confederation political landscape?) and invite further immigration from Europe.
Next you'd need more of an industrial boom in the 1910s-1920s to foster economic growth.