Are there nonstop flights from Rosario (RSJ) to Seattle (LKE)?

Yes. Kenmore Air fly this route. Flight time is about 38m.

Rosario → Seattle

Rosario Seaplane Base (RSJ) to Kenmore Air Harbor Seaplane Base (LKE)・120 km

Nonstop flights available (1 airline). Flight time about 38m. Nonstop return flights also operate.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.