Anglo-American is far, far too easy. So let's go for an early POD and make something more "alien".
Caribou pastoralism arises in Alaska among the Dene peoples between 1000 BC and 1 AD. This includes increased plant usage. This spreads to the people of the Alaska Panhandle, who are pressed by the inherent environmental problems (being mountainous and rugged) and end up intensifying this plant use in their own caribou pastoralism, adding in water plants (most critically
sagittaria cuneata aka wapato) and some other plants--water plants are helpful since water is plentiful in a temperate rainforest. This combined package of reindeer pastoralism and combined water/land plant usage spreads down the coast to the Haida, Tsimshians, Wakashans, and Salish peoples, until it reaches its limit somewhere in Northern California due to lack of water/irrigation and more critically, too many competitor species for caribou (such as deer, which carry parasites deadly to reindeer). In most of western Washington/Oregon as well as Idaho, they'll be confined to the rivers, since it's difficult to actually farm most of that area without good ploughs/irrigation works (which they may very well get later on). Other key domesticates would be moose (at the very least tame specimens used like elephants), mountain goat (demand for their wool leading to domestication), ducks (mallards were domesticated in the Old World), and Canada geese (naturally drawn to humans, fully domesticated by breeding them to be incapable of flight). In areas where agriculture is too poor to function, like in most of northern BC, pastoralism dominates, but in other places like the Willamette Valley and coastal Washington, more agricultural communities begin to emerge.
Key in their development is the increase in metalworking due to higher demand. While copper had been worked since even before our POD by the peoples of the Copper River, the increased demand leads to the eventual discovery of smelting and thus true metallurgy. Copper working spreads down the coast, although Alaska remains the main center of it due to the rich deposits and antiquity of its use. Gold and silver are also increasingly used, mostly for ornamentation and ceremonial use. This development may occur 500 - 1,000 years after our POD. At some point, they may think to combine it with tin, which is rare in North America. However, Alaska appears to be rather rich in tin, having some placer deposits in the Alexander Archipelago, along the Yukon, the Alaska Peninsula, and especially the Seward Peninsula. So perhaps after a few centuries of increasing use of copper (including perhaps some arsenical bronze use), alloying it with tin becomes the prefered method of metalworking, thus a "Pacific Bronze Age" begins. People will come from far away to trade for the tin or for bronze goods, increasing the development of naval technology in the region. Perhaps at some point, better sailing tech is applied to these ships and thus longer voyages become worthwhile.
The second key is the expansion of various groups, the most key group for our purposes being the alt-Tlingit. They may be the first to work bronze. They are already skilled seafarers and whalers, as with many coastal groups. And now they have poor islands and a high surplus population. My guess is the trigger would be a major local volcanic eruption, such as
Mount Churchill's 750 AD eruption. Entire families would be moving elsewhere, and bitter warfare would result. Combined with being middlemen for the tin trade, they would have a desire to eliminate any potential rivals (Aleuts, Dene peoples, etc.) so could take their land. Farming in that region will be difficult (it's never warm, although never bitterly cold either), but possible to get a small harvest (whaling and sea life is of course the real sustainer of things) on some islands--reindeer pastoralism and fishing/sealing/whaling would be the main lifestyle. They may continue pushing west, blending with, absorbing, or displacing the Aleuts, and settling empty islands. In a few centuries they'd reach the Commander Islands, and from there come into contact with Kamchatkan peoples like the Itelmen and Koryaks.
This forms a trade network from Vancouver Island or so to Kamchatka. The Kamchatkans have goods from further south, including iron goods, which they may exchange for bronze, precious metals, and other goods from Alaska and even further. Soon, the Ainu are linked into this network, and from there, this attracts the attention of the Japanese, who notice the Ainu are rather wealthier than before. It's about 2,500 kilometers from Honshu to the Commander Islands, so they aren't likely to meet the Japanese directly, but they may know something's up. It isn't impossible to farm in Southern Kamchatka, so crops used by the Ainu (millet, buckwheat) may be used more by the Itelmen, while whatever crops make it to the Commander Islands will also be adopted by them. Likely the domesticates will cross over as well (including new reindeer breeds). Ainu crops may cross back over to the New World, and perhaps some cultural innovations (like the wheel).
We're now at around 1250-1300 AD. Let's have the Mongols do much better in Japan, causing a major cultural shock and change there. The Mongols/Yuan Dynasty will also find the increase of gold and silver among the Ainu, and may send their own expeditions that way, so rule of their tributary tribes in Hokkaido and Sakhalin may be a bit tighter than OTL. Mongol rule is brief, but by the 15th century whatever Japanese state has emerged from the ashes is probably going to be more wary of the world around it, and first on their list of peoples to conquer are the Ainu. Being wealthier, but perhaps not much more powerful or united than OTL, and not too close to China, it could be argued that conquering them would be a fantastic idea. More land, more people to tax, distracts the provincial lords (and rewards them for their efforts), etc. Once the Ainu are subdued, the Japanese are now even closer to the Bering Sea trade network. They may begin tapping into that, for sea otter furs, walrus ivory, antler velvet, gold and silver, etc. Of course, they'll be extensively fishing in that area as well. Direct rule isn't likely north or east of southern Kamchatka (environmental issues, etc.), but at this point that doesn't matter. What matters is they now have a clearer picture of what the northern barbarians have to offer, and will know about the Commander Islands and Aleutians. This is where they first come into contact with the Tlingit.
There may very well at this point start an age of exploration in that region. What starts with new fishing grounds and some trinkets leads to the discovery of full-on
civilisation in the Pacific Northwest, where at least a few million people will live, and cities as large as 50,000 people or more may exist. At this point, there would very likely be actual states in the region, if not full-on empires. This is a group much more worthy of notice than some barbarians who live on miserably rainy islands and build good boats. The situation in Japan, where the elite would want more people to tax, distracting the elites from internal intrigues/wars, and a population which was often very stressed due to the lack of land, means it isn't implausible that you may get some attempts to establish rule over the area, starting with coastal southern Alaska. There's not many situations better for a group of greedy "conquistadors" to sail in and start cracking skulls in some places. Similar to Mesoamerica, the likely tactic would be subverting these states by internal rebellions (including slave rebellions), allying with their neighbours, and just pure shock--firearms, cavalry charges (they aren't likely to have any concept of riding animals for warfare), and strong armour (bronze armour/weaponry will be rare). Once an initial foothold is gained, the rest will fall in time.
Like Mesoamerica, it will likely take a few centuries of warfare and subversion of various native states and peoples, and the frontier (Yukon, interior northern BC, Nevada, etc.) may not be tamed until the 19th century. But this will be a full Japanese conquest of the Pacific Northwest. I'll leave out what happens in California--it's likely to be a peripheral region to the main PNW civilisation due to the environmental issues. How the "Cascadian" Japanese culture evolves could go in any direction--they'll have a large number of "Mestizo" people, some remaining indigenous groups, but also a lot of Japanese settlers ranging from elites moving there to own more land to the desparately poor and disadvantaged peasants to monks to wealth-seeking merchants. They may peacefully "separate" from Japan in a way similar to Canada or Australia. Or they might have a war of independence due to some political issues with Japan. Any number of things could happen. Since you didn't include Alaska in your OP, we could have the area be divided in two somewhere around 52 N or so. It's reasonable--Alaska/northern BC will have different needs than the more populated south, so might as well divide it up.
It's possible China or Korea could do something similar, but it feels most natural for Japan to do this due to geography. The other candidates would be a native empire from the Snake River Plain to Vancouver Island surviving and modernising, or being conquered and gaining independence, or the entire area falling under the control of a single European power and gaining independence as one state. In any case, I don't think it's plausible for it to be anything but Anglo-American (unless you have a French-Canadian wank) without an early POD and stronger local civilisations.