Switching barrels = yes (in some cases).
You cant swap from AEG to GBB though, but you can for example swap a 11.5 inch barrel on an aeg and swap it for a 14.5 inch AEG barrel, and you can swap an 11.5 inch barrel in a GBB for a 14.5 inch GBB barrel.
Western Arms and WE are the big GBBR brands in Canada (and the states) and parts are not to hard to find. But both have little problems just like any other gun.
What GBBR are you thinking of getting/have?