In a recent interview with GNN Taiwan, Game Freak’s Junichi Masuda confirmed that Pokémon can be transferred to Pokémon GO from Pokémon Let’s Go Pikachu and Eevee. During the same interview, Masuda also mentioned how throwing a Poké Ball is performed in the upcoming Nintendo Switch games:
Pokemon can be transferred from Let’s GO to Pokemon GO after unlocking a certain story episode. When using Switch as a handheld, you use the Gyro sensors to aim at the Pokemon, then press the buttons to throw your Pokeball. We thought if using touchscreen, but you can’t hold the Switch well with one hand, so we scrapped it.
Source: GNN Taiwan