I've successfully gotten the game to run in 4k, ultrawide, etc https://onedrive.live.com/?authkey=!AA4 ... BE675!1622 but if even one byte of Viva Pinata.exe is changed Games for Window Live doesn't work and thus prevents saving.
Alternatively you can change the resolution while the game is running with Cheat Engine but that breaks menus unlike the hex edit.

How to do the hex edit to Viva Pinata.exe:
Replace all instances of
80 07 00 00 B0 04 (1920x1200)
with the desired resolution. For example, 4k:
00 0F 00 00 70 08 (3840x2160)
Resolutions that aren't 16:9, or 4:3 (game squishes 16:9 for 16:10) require replacing 39 8E E3 3F with the desired aspect ratio. http://www.wsgf.org/article/common-hex-values
The HUD/UI will be stretched, though.