You can write this:
Pair v = *find_if(m.begin(), m.end(), [](const Pair & p) {
return p.second == 3;
});
You don't need to capture it to begin with.
BTW, you should not assume std::find_if
will find the element. A better way is to use iterator:
auto it = find_if(m.begin(), m.end(), [](const Pair & p) {
return p.second == 3;
});
if (it == m.end() ) { /*value not found*/ }
else {
Pair v = *it;
//your code
}