Best Buy Canada is preparing for E3 with a special store page that has gamers saving 20% on all pre-order games during E3 2017. The E3 hub does more than just offer savings though, it teases announcements from Microsoft and Nintendo, but not Sony.
The Sony hub is filled with previously announced games, while Nintendo and Microsoft are listed with coming announcements.
All the placeholder box arts I found (with help from Reddit) for the Nintendo Switch are Skyrim, Dragon Quest XI, Minecraft, SSB, Pikmin World, and Xenoblade Chronicles 2. As for the teased Xbox titles, Best Buy's placeholder images are Fable Legends and Phantom Dust.
The placeholders are likely based off of a previous retailer listing that prepared a number of box arts in case they were announced.
Basically, we should just prepare for new games, like we get at every E3.