I've never had a problem with putting a rolling tote under the seat in front of me on a commuter plane as long as I sit on the side with 2 seats (for the E145) and it's not the first row of the plane. There's more room under the two seats than under the seat of a mainline jet, especially compared with the amount of room under Boeing Aisle seat or a plane with DirecTV. I"m pretty sure it also fits in the overhead of a lot of small planes also although i can't remember for sure regarding the Q400/E145. I am sure about the under seat storage for the double seats because there is no bar or electronic equipment taking up space. It also seems as if it will accommodate a taller bag than a mainline jet.

If you're concerned about it, I wouldn't book row 2 on the E145 either. On some planes (I can't remember which type of small plane this happened on) Row 2 is the first row even if the seat map says there's a Row 1 on the right side. I think it has to do with whether the bathroom in the front or the back. Anyway, I've had row one before only to find that row 1 doesn't exist and I'm really in row 10 for that a/c.

That's a long winded way of saying "No, I don't think it will need to be gate checked"