As crazy and as pissed off as you will get at me for saying this, but personally I wouldn't use either!
The Dawes is too old in my opinion to be reliable, i make that statement because I don't know how many miles are on the Dawes, and you would have to make sure it completely renovated to make touring trips on it; looking at the geometry of the frame it doesn't have the look of a long distance touring bike, the wheelbase seems more in tune with a sport frame bike due to it's shorter stays then on a touring bike, the frame is too compact for touring, the trail is too short due to the steeper headtube angle; I hate strap on water bottle cages, the ones I've ever tried kept shifting as I rode, I never go back to strap on cages.
The Btwin is a lowend bike that on a touring trip could result in all sorts of breakdowns, another more of a compact frame that wasn't design for touring as the components tell that same story; aluminium frame can be uncomfortable on long days of touring miles plus AL frames are more difficult to repair in the field, and that one wasn't designed to hold touring stuff.
I'm sorry for the negativity, but if I were you, which I'm not, I would find another used touring bike that hits all the checkpoints you want, one that is a bit newer, or at least in excellent condition, from no older than the mid 80's when steel hit their stride as did friction components, even the index units they had back then could be turned off so you could use the system in friction mode. I would also find one that uses cantilever brakes, or on newer bikes V brakes, either of those two brake styles will allow you more room for fatter tires and fenders without clearance issues. Old bikes may have 27" tires but Schwalbe makes a fantastic touring tire in that size called the Marathon Greenguard
So the last two tours I've been on I've ridden my first road bike love, my B'twin Triban 3. We've been to Wales and Scotland together, here's a photo of it in the Cairngorms:
View attachment 454913
Ah, happy memories

In the past 6 months or so there's a new steed in town, my 1984 Dawes Galaxy.
View attachment 454914
Of course, this is specifically designed to be a touring bike.
So here's the question, what bike would you, if you were me, use on your next tour? Here's the pros and cons as I see it:
Triban 3:
Pros-
- Relatively light.
- Two fully functional bottle cages.
- Indexed shifters (possibly a con if I was going abroad far away, but I'm not).
- Very familiar with the bike.
- QR skewers front and rear.
- Standard 700C wheels.
- I've got a 30t cassette which together with the triple chainrings means it's great for going uphill
Cons-
- Can't mount a front rack due to carbon forks.
- Not designed as a touring bike in the slightest.
- Indexed shifting is nice until it stops working.
Because I live in America finding the exact specs on the Btwin is a bit difficult. So my concerns are from lack of specs to figure it out if there is concern.
First off when you tour you need to make sure the equipment is up to the task of the long haul and if the bike parts will hold the extra weight.
So my first concern is the wheels, this is one of the major weak spots of touring bikes, so if you are considering going to 700c wheels you first need to make sure the brake calipers will reach the 700c rim. Secondly, if they do or do not reach you need a set of wheels that will hold up to touring, and I would suggest going 32 3 cross spoke rim in the front and 36 3 cross on the rear; some will suggest 36 on the front but you will only need that many on the front if you plan on carrying more weight on the front other than a hand. If 700 wheels will not work then going with 27 inch wheels is not a bad deal because Schwalbe makes a superior touring tire that is also the lowest rolling resistance touring tire on the market called the Marathon Greenguard HS 420:
https://www.schwalbetires.com/bike_tires/road_tires/marathon_420 This tire is an extremely puncture resistant and long wearing tire, I use those on my now dead touring bike and had about 3,000 miles on them and didn't even look worn, nor did I have any flats. In that same thought you need to get better hubs that are sealed, probably Shimano Deore hubs would fit the bill really nicely and they aren't expensive. Also spoke wise I would just go with a good quality brand round straight gauge spokes, no need for double butted, and use brass nipples for the long haul, round spokes and brass nipples are also cheaper to build with; Pillar spokes are really good and cheaper than other brands. Rim wise I would ask a few bike shops what they recommend, Sun CR18's are pretty good for touring.
Next issue is the brake pads, standard brake pads are crap in the rain so you should get a set of Kool Stop with all Salmon coloring.
IF after replacing your pads (you'll need to do a fully loaded test ride at a high speed and brake) and the brakes are not feeling secure enough for you then you may need to new calipers, cheaper quality calipers can flex which is not good when you have a loaded bike. If you run into that problem I would get a set of Shimano 105's these are the best for the money and they don't cost all that much.
Another weak spot is the bottom bracket, on cheaper bikes the bottom bracket won't be a sealed version and with touring rain can get into that area and then you will have problems. Again Deore makes a really good one.
And since you will be replacing your fork you should seriously think about getting a better headset like Cane Creek 40, or if you want the absolute best bombproof headset, which this model is actually the best for CF forks because it supports the steerer better than any other headset which could be critical for a CF fork used in touring, and that's the Cane Creek 110.
You need to check the condition of your cables and chain to make sure they are good for touring on. If you have to replace the chain I would buy a stainless steel chain like the Connex.
I know this stuff cost money but some of it you were already thinking of replacing wheels and the fork well then you have to do that anyway so make sure you get stuff that will hold up to the weight of touring gear and hold up against weather.