I agree with other answers that going by land through Alaska and Siberia and crossing the Bearing Strait at a relatively narrow point might be much better for your invaders than crossing hundreds or thousand of kilometers or miles of the Arctic Ocean.
Crossing the Arctic Ocean can be quite dangerous.
If they cross in groups using dogsleds they will have to carry food and other provisions for themselves and their dogs. Considering the distances involved, they should have to establish several supply depots and make several expeditions to stock the supply depots before before there are enough supplies accumulated in the depots for the group to be able to cross the entire distance.
As I remember, using pre stocked supply depots was necessary for the expeditions to the North Pole and the South Pole, and those expeditions had far fewer members than the total 1,000 of your invaders if they all go on one trip. And a route from Canada to Russia over the ice might be much longer than a trip to the North Pole and back.
With their greater than human endurance your invaders might not need dogsleds and might be able to carry all needed supplies in their backpacks. But you should calculate how much food they would need during the time necessary to cross the Arctic Ocean and whether they can carry that much weight.
Crossing the Arctic Ocean ice on foot is often very difficult because the ice is very rough in some places and there are open patches of water in other places.
The Arctic ice melts and covers a smaller area in the summer and reforms to cover a larger area in the winter. And with global warming the Arctic ice gets smaller every year. Thus the prospect of sailing cargo ships across the Arctic gets closer every year.
So possibly your invaders could paddle kayaks across open water between the northern shores of North America, Europe, and Asia and the southern edge of the ice sheet. I imagine that there are many icebergs and ice floes floating around in those waters.
And possibly people might get suspicious of many kayaks traveling in unusual directions. It's not like there are actually unknown and undiscovered tribes of Eskimos without Russian, American, Canadian, or Danish contacts and citizenship lurking behind every cape and island in the Arctic. All Eskimo groups are pretty well known and some members of them might have satellite phones capable of reporting strange people in kayaks to the authorities for all that I know.
You might not know any Eskimos personally, or the locations of specific Eskimo communities and hunting grounds, but many outside people who travel in the Arctic will know where Eskimos are usually found and might often have contacts with Eskimos, and might notice strange kayaks making strange voyages.
Or your invaders might want to use larger boats or ships. Possibly they could buy an icebreaker and start a passenger service from Canada or Alaska to Siberia & back. And possibly their voyages could sometimes carry invaders hibernating or something in the cargo hold to be woken and secretly released near the coast of the destination.
Or maybe your invaders might use submarines to travel under the Arctic Ocean, just as drug smugglers have been known to use privately made submarines to carry drugs. An atomic submarine could travel all the way under the Arctic without ever having to come to the surface.
Acquiring or building a conventional diesel electric powered submarine or submarines would be many, many times easier and less conspicuous for your invaders. But submarine batteries can store only a limited amount of electricity and power the sub for a limited distance before they run out of power. Then the sub will have to surface and run the diesel engines using outside air (instead of the limited air on the sub) to recharge the batteries until they are fully charged and the sub can submerge again.
Thus the sub will have to travel mostly though ice free waters, since the only ice covered waters it will be able to travel under will be patches short enough for it to make the trip on one battery charge, or else where they will be certain they can surface and break through the ice, and I don't know if they will be able to predict ice thickness that well.
And if the sub travels under ice free water, it will have to worry about running into the sea floor, or ramming into an island, or hitting a submerged part of an iceberg, or being accidentally run over by a ship, etc., so they will have to navigate carefully.
And the sub will have to scan the surrounding carefully to make certain nobody is around to see before coming up to run the diesel engines and recharge the batteries.
Depending on how many trips your invaders make and how many people make each trip, they might try several different travel methods and different routes to travel between Canada and Russia.
About:
they can starve, orcas and white bears consider them delicious, but, on the same time - raw orcas and white bears meat are considered edible by invaders too.
Polar bears on the hunt will attack humans, but humans are apparently too strange and exotic for most wild orcas to hunt, as the very few recorded possible attacks show:
https://en.wikipedia.org/wiki/Killer_whale_attack1
As for eating orcas and white bears, Arctic orcas and white bears would usually be found only where seals would be found, and hunting seals would be a lot less dangerous for your invaders.
Orcas, like other cetaceans, are extremely intelligent. It is quite possible that the intelligence range of orcas and many other cetaceans overlaps considerably with the intelligence range of humans, and that an objective outside observer might consider orcas and other cetaceans to be intelligent beings and people, or as much so as the observer considers humans to be.
Even though it would not fit the definition of cannibalism exactly, eating human beings should seem almost as disgusting to the invaders as eating members of their own species. And eating orcas should seem almost as disgusting to the invaders as eating humans. If your invaders would kill orcas to eat they are very evil and unscrupulous persons without strong ethical codes.
