Sour cherries are incredibly tart without sugar, and it sounds like both your cherries and your concentrate are unsweetened. You can try adding these to cakes unsweetened, but it may be necessary to sweeten both of these before adding them to cake formulas.
My first thought was actually of an angel food cake, it is white so you’ll get the pink color you’re after, and it may be sweet enough to counteract the cherries and juice. However, when someone takes a bite of the dried cherry, it may come across as too tart/jarring, not sure how that would be. It would also have a nice spongy texture that would be nice with the pool of cherry sauce that you’re planning on serving it with. And angel food can be baked in a loaf pan.
My next thought was Rose’s white velvet cake, subbing a small portion (1-2 Tbs) of the cherry concentrate for some of the milk. Normally, you would think of pound cake in a loaf pan, but you need the higher sugar level of a layer cake formula. You might try soaking the cherries in Lyle’s syrup or corn syrup in order to both hydrate and sweeten them. Syruping the cake with simple syrup may help correct the sweetness level.
My last idea was a bit different, that is to use the cherry concentrate in Rose’s red velvet cake in place of the red food dye. That would add a whisper of cocoa and brown sugar to the cherries. It won’t be bright red like the food dye version, probably more brownish-pink.
Whatever direction you try, please post back with your results!