During the Nintendo Treehouse Live Stream at E3, one of the Staff that demonstrated Splatoon 2 mentioned that the game will run at 1080p & 60 frames per second (Handheld mode will be only be 720p). Splatoon 2 producer Hishashi Nogami then confirmed that it was indeed correct.
The Treehouse team also got hands on with the Salmon Run mode in Splatoon 2 and showed that the difficulty of the mode can go as far as 200%. You can see for yourself below.