It says that the goverment made him join their side, and he works for special operations. Does that mean he wasn't part of the Anti Umbrella movement? I doubt that he would have time with his busy life as a agent for the goverment right?

I'm a bit hazy on details, but wasn't the Anti-Umbrella organization only featured in Gaiden?

If so, that means it isn't Canon.

Yeh, after Gaiden failed horribly i think they cast it to one side and pretended it didnt happen.....at the end im sure Leon was supposed to be a monster in disguise or some rubbish like that. So its not canon, in story line terms Gaiden never happened. He is a government agent :)

Ya it sucks i know

Leon came into contact with an anti-Umbrella organization. But exactly what capacity he was involved with them in is unknown, he was not an agent for one like Gaiden depicts.

Since he was in the US government, it was probably the Anti-Umbrella Pursuit and Investigation Team featured in Dead Aim (which is Noboru Sugimura's take on Gaiden).