Looking to make the coordinate system shift in ArcMAP (for Nova Scotia) between ATS77 MTM 5 and NAD83 CSRS...NTv2 file?
No, you don't need to, but you will need the NTv2 transformation files for New Brunswick. They're available for download from GeoNB.
The file you're interested in is NB7783v2.GSB. Once extracted from the downloaded zip file, place it in your ArcGIS home, pedata\ntv2\canada.
EDIT: Okay, so most of the information above is incorrect because I assumed New Brunswick and Jason in interested in Nova Scotia. Nova Scotia has a different NTv2 file, and you may need to purchase it. It is listed on the a price list. The referring page mentions that a data use license is required for NS778301.gsb.
On the other hand, Service Nova Scotia has an online coordinate transformation service, but it only takes GML, Text, or keyboard.
General information: NTv2 (National Transformation version 2) is a gridded file of offsets between two geographic coordinate reference systems. In this case, they are ATS77 and NAD83 (CSRS).