Simple Q&A Pathfinder (By RAW) I

[Prime32]

Q31:

How exactly does this work? Can a large creature only carry a cannon around like a two-handed weapon, or can he shoot it like a nomal two-handed gun? if so, can he use feats that normally only affect two-handed guns?

There's some debate there. It seems he can use it in all ways like a two-handed firearm except for loading. Maybe.

Q32: Is their any way to load a siege weapon faster? Does counting as four crewmembers for being large allow you to load and aim as if you were 4 guys?

http://www.d20pfsrd.com/feats/combat...ngineer-combat
An lv11 gunslinger can make use of Lightning Reload on siege firearms, and the musket master archetype might also help.
As for the second part, yes but this doesn't affect the number of actions needed to aim/reload.