Wildlands cannot be played without being online even in offline mode, you can't use the trainer if you're online, really genius.
Incorrect. Run game in either online or offline mode (Steam and/or Uplay). Once at Main Menu, alt tab to desktop. Right click run as admin on trainer. Alt tab back to game and unplug internet or disable network/internet connection. Press F1 to activate trainer. Play campaign mode as normal, just bypassing any messages about not being online.