Gun Training (Ex)
Starting at 5th level, a gunslinger can select one specific type of firearm (such as an axe musket, blunderbuss, musket, or pistol). She gains a bonus equal to her Dexterity modifier on damage rolls when [b]/b]firing that type of firearm. Furthermore, when she misfires with that type of firearm, the misfire value of that firearm increases by 2 instead of 4. Every four levels thereafter (9th, 13th, and 17th), the gunslinger picks up another type of firearm, gaining these bonuses for those types as well.
As per the Gun Training ability, you're only add your Dex modifier to attacks made when firing a gun, and swinging the sword cane part of your pistol doesn't qualify as 'firing'. So you'd only add your strength when swinging your gun as a sword cane, but you'd add dex if you fired your sword cane pistol as a gun.
Pistol Training (Ex)
Starting at 5th level, a pistolero increases her skill with one-handed firearms. She gains a bonus on damage rolls equal to her Dexterity modifier, and when she misfires with a one-handed firearm, the misfire value increases by 2 instead of 4. Every four levels thereafter (9th, 13th, and 17th), the bonus on damage rolls increases by +1. At 13th level, a pistolero never misfires with a one-handed firearm.
If you're referring to the above class ability of the Pistolero archetype for the Gunslinger, then you might be able to do dex damage even if you used the sword cane pistol as a sword, rather than as a gun, but that could be subject to GM interpretation given the class that the ability is built on.
I was referring to the Later.
Well then, from reading the Pistolero Pistol Training ability, I'd say that as written you could get dex damage added to your damage roll when using the sword cane pistol as a sword cane, allowing you to add both your strength and dex to the damage roll as a melee weapon. I'd say that's a decent enough reason to use the sword cane pistol, so I'd say go ahead and do it. Though some GM's might rule that the EX ability is intended only for use with pistols being used AS guns, the ability only states that you do the extra dex as damage when using a one handed pistol, not that you have to use the pistol as a gun.
So far as I can see, this would be a legit weapon to use for PFS even, though don't quote me on PFS rules, as I don't play with PFS often.