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The Canade-United States border is the longest border in the world.
Asia is the continent that has the longest land border.
mississippi
Kazakhstan and Russia share the second longest border at 6,846 km
paraguay
Alaska borders on the Canadian province of British Columbia and the Canadian territory of Yukon.
Alaska is bordered by the Canadian province of British Columbia. It also is bordered by Yukon, a Canadian territory.
The province of British Columbia and the territory of Yukon Territory border Alaska.
British Columbia and the Yukon Territory.
The Canadian province of British Columbia and Canada's Yukon Territory border Alaska to the east.
nice question if you mean longest & continuously in the geographical & or geometrical sense then it is apparently Ontario since the british Columbia borders with the united states don't appear continuously shared in a manner of speaking because they are discontiguous tho they are in total length longer than ontarios but if you mean longest & continuously in the chronological & or historical sense then it is apparently a triple dead heat among Ontario quebec & new brunswick since they are the oldest provinces on the border & indeed of exactly equal age & if you mean longest & continuously in both the above senses at once as you appear to because the province you seek could appear as you've described it in both senses & likewise if you really mean which single province rather than which provinces as you also very much appear to then the singular answer you seek indeed appears again to be Ontario
Alaska is bordered by the Canadian province of British Columbia. It also is bordered by Yukon, a Canadian territory.
Alaska borders the territory of Yukon and the Canadian province of British Columbia.
Not states but the province of British Colombia and the territory of the Yukon.
Yukon Territory
The province of Alberta and the territory of the Yukon.
Ontario, we have no northern provinces.