They are the two currently strongest countries so yes it is very safe to say they are the best rivalry. If it was two other countries that were clearly tier 1 it would probably be them.
Russia has barely done shit in 30 years. Struggle to develop quality top 6 Cs and top pairing true #1 defenseman. The Russian W and G groups however you could put up against anybody in my opinion. Especially in net, whatever they put in their borscht is producing some seriously great goalies. All of Sweden, Finland, and the Czechs are all capable of beating anyone on any given night in best on best. I don't even think Canada or the States would be considered heavy favourites against them everyone healthy. Slovakia, Germany, and the Swiss punchers chance kind of teams. Routinely now can get a player or two from one of these countries in the top 15 of the NHL draft.
As a Canadian hockey fan I got to say I absolutely f***ing love to see it, hockey is a great sport with tons of incredible athletes. We'll never have what soccer has internationally but the quality of the competition at the next Olympics should be high. I do hope by then whatever nonsense can be sorted out in Europe and the Russians can participate. As much as it sucks to have not seen McDavid or Makar or MacKinnon at the Olympics, Nikita Kucherov hasn't put on his nation's sweater since the WJs either.