You should have no problem carrying on a big suitcase onto acela. If you can get a redcap, that will help.

These are the dimensions for carry on bags allowed on amtrak:
2 Bags — 50 lbs. — 28" x 22" x 14" Each

source: http://www.amtrak.com/carry-on-baggage

That is actually a much bigger bag than allowed as a carry on a plane.