I've often either been in a CR9 sandwiched between an A319 and a 757, or been in a mainline jet next to a CR9. They frequent the C and D gates. If you were to check the stroller through, it's worth noting that D to C and C to B are pretty equidistant, and there should be a moving walkway from D-C and C-B (but the last flight I had out of a B gate was on WN, and that was years ago).