More can be written, but you might like to start with the FAQ page on North America, specifically 'How come America was not "discovered" via the Bering Strait?' by /u/Reedstilt. For when any part of the Far East became Russian, you might look for the mention of Dezhnev. For native contact, I also found "Russia is so close to Alaska, why didn't the Russians discover North America well before Columbus?" by, appropriately enough, /u/The_Alaskan.

This is not to discourage discussion. More questions, data and debate are welcome.