I imagine quite well to start with in OTL Canadians were bad ass fighters in the first world war and they would be on their own ground.
As for once American industry is up to speed really depends on how quickly we knock france out and whether any of the central powers (or possibly Mexico) are willing to help us hold the empire together.
Chances are we would have to come to some sort of settlement eventually but if German and Austrohungry stick with us then we might be able to get enough of a victory to have the canadian border reset to pre war bounderies, just paying compensation once the US is on it's own.
Every Commonwealth Soldier Fighting in North America, is One Less Fighting in Europe ...
How Long Before British Troops Hafta Be Sent in to Tip The Balance Back in their Favour ...
What if NEITHER Theatre Can Be Tipped in their Favour, What then?
Renew? It didn't have any claims to begin with, let alone at the beginning of the 20th century.
The Relevant Treaties Weren't Even Signed Until The 1840s, with The Border Along The Strait of Juan de Fuca Not Being Completely Decided Until 1859 ...
That's Only 60 or 70 Years Ago from The Viewpoint of The Teens ...
I Can See 54' 40" or Fight Changing Over Rather Readily to, We've Changed Our Minds Dammit we Want it ALL!
Actually, Germany never lost telegraphic access to Washington at the outbreak of the Great War. How else was Zimmerman to send his telegram to Mexico or the Germans to warn that any ship in the war zone was subject to attack by submarine? The British did however monitor German communications traffic between Berlin and its embassies overseas.
In One of The Lesser Known Build Ups to The Great War, The British Government Cut The German Transatlantic Cable at The Azores ...
From then on All German Traffic to Washington had to Go Over British Wire at Some Point in its Transmission ...
Moreover The Americans were FAR Too Polite to Read German Diplomatic Traffic Going Over Anybody's Lines, The British had No Such Compunctions!
But if Britain is supporting Germany then how long would the French last?
I mean would the Americans get there in time?
The REAL Question is, How Long Can Britain Maintain The Balancing Act ...
It'd Be Like The War of 1812 All Over Again ...
Would The British Get to Canada in Time?