I'm currently playing as the Spanish. I have taken quite a lot of land and some pretty advanced troops. I just aquired the abilty to produce gun powder units. I have some primative cannons now which absolutely annalitated the enemy's wall (I see why they say walls are pointless vs guns).

My question is, what advanage do the more advanced cannons have, and how do I produce infantry armed with guns (muskets, primative rifles, etc.)