First of all, I cannot help but point out a practice I consider bad in the way you defined your question. You are comparing a class of algorithms with a class of problems. Although closely related, they are not the same. As an example, consider the halting problem. It is a very well defined problem. However, we know that no Turing Machine can diagnose it. Given the Church-Turing thesis, this is the same as saying that there is no algorithm for this problem.
However, one can rephrase the question such that the items compared are of the same nature. Consider constraint programming (CP) as the computational model A and
boolean formulas as the computational model B. I chose boolean formulas because SAT is probably the most known CSP and furthermore boolean formulas have a nice property, which I will use below.
Although I have programmed in Prolog, I cannot say I have a good knowledge of constraint programming. However, I am almost certain that they are Turing-complete. Since they use constraints, one could use them to "simulate" head moves,e.g. if [constraint] then move to this cell . Furthermore, one could write contents into that tape. Therefore, constraint programming is as powerful as Turing Machines. Since all programs in CP are algorithms, they can be simulated by a universal TM. Thus CP and TM have the same expressibility.
One might think at this point that CP is a stronger model that boolean formulas. However, in Arora and Barak's book "Computational Complexity:A Modern Approach", in chapter 2, a proof is given that any boolean function has an equivalent boolean formula ( the theorem is labeled "Universality" of AND,OR and NOT). On a given input, the formula is satisfied if and only if the boolean function is true for this input. As an informal proof, consider that those 3 operators can express any piece of hardware. Furthermore, every other input can be translated into a boolean one. Therefore, every TM can be simulated as a boolean formula. Thus boolean formulas are Turing-complete. Furthermore, there is a TM that can diagnose the satisfiability of a boolean formula. Therefore, boolean formulas and TMs are equivalent.
It follows that the two models have the same expressibility.