OK, it sounds like you have this all pretty much in hand. I'm still not quite sure I understand the A-C at EWR reference. If you are on the direct flight EWR-DBV, then you wouldn't be on an Air Canada aircraft at all. You would come from CVG, possibly the day before, and just have a direct departure from C.

Tight but doable is indeed the best way to describe it. If you can in any way reduce the number of flights that would be great, but I guess you are left with what you have booked. Keep an eye out for space on the direct flight, is probably my best advice. Oh, and AC doesn't have F, just J, but in most respects equal to the new Polaris seat on UA.