I ask this because I've noticed in a few games that I've played that the demo units tend to be Scottish. In Company of Heroes, a WW2 RTS game, the British faction's sappers are Scottish. In warcraft 3 the sapper units, mortar teams, and the Dwarves in general (which tend to favor weapons that go boom) speak with Scottish accents. And of course Team Fortress 2 with its Demoman class who is a Scot.
Just curious where this trend came from.
I'd argue its coincidental and mostly the result of artistic licence.
The only evidence I've come across of the British army deliberately seeking out men from particular geographical areas for specialised engineering task is in the First World War's Tunnelling Companies. These however where drawn primarily from Wales, the north of England and London (London underground construction).
However as you mentioned Company of Heroes, I'm going to focus upon the Second World War. In terms of battlefield demolitions, this would be handled by an infantry battalion's assault pioneers platoon, or units of the Royal Engineers (R.E.) organised as Divisional support troops, as part of 79th Armoured or an A.G.R.E. (Army Group, Royal Engineers).
Infantry battalions and R.E. companies/squadrons were localised under the Childers reforms of 1881, bound to recruit and garrison a regimental depot in a particular area e.g. the regiment for the counties of Argyll and Sutherland was The Argyll and Sutherland Highlanders etc. etc. if these units were to form part of an infantry division, These units would then be brigaded alongside regiments usually from the wider region, and the resulting division was named after the increasing broader geographical area e.g. the 44th Lowland, the 46th Highland and the 227th Highland Brigades resulting in the 15th Scottish Division (As of 1944).
79th Armoured and A.G.R.E.s were more nationalised in their make-up, and I have seen no evidence to suggest that the British army deliberately set out to recruit Scotsmen into the R.E.s, or aimed to put Scottish units into these formations.
In the case of Company of Heroes, 15th Scottish Division was one of the principal divisions deployed in operation EPSOM, tasked with taking hill 112 as depicted in the game. As this is the mission where sappers are introduced to the player, it would seem that the designers attempt to give the player of flavour of the battle through voice acting. Equally, the clearance of Caen was handled by II Canadian Corps which consequently led to Royal Artillery crews with Canadian accents.