Use a non-const variable as an index into a constexpr array to pass to a template parameter

I have an constexpr size_tarray whose members will be passed to the template parameter of an initialized class, iterating through the array to construct and use several different templated objects. Here's the general idea:

template <size_t N>
class Foo
{
    // magic
};

constexpr size_t c_arr[] = { 2, 5, 3, 2 };

for (int i = 0; i < 4; i++)
{
    Foo<c_arr[i]> foo;
    foo.bar();
}

However, this throws the following error:

templ_arr.cpp: In function ‘int main()’:
templ_arr.cpp:56:21: error: the value of ‘i’ is not usable in a constant expression
         Foo<c_arr[i]> foo;
                     ^
templ_arr.cpp:51:14: note: ‘int i’ is not const
     for (int i = 0; i < 3; i++)
              ^
templ_arr.cpp:56:20: note: in template argument for type ‘long unsigned int’
         Foo<c_arr[i]> foo;

I can't seem to find a way to use const_caston ito allow it to be used within a parameter, nor can I fix it by doing something like this as it gives me the same error:

for (int i = 0; i < 4; i++)
{
    const int j = i;
    Foo<c_arr[j]> f;
    foo.bar();
}

What am I doing wrong and how can I fix this?