Various people on the AtlanticRails and RailsNB mailing lists have reported a CN test train in Nova Scotia and New Brunswick. CN 2517 and the two test cars, operating as train 482, worked the Dartmouth subdivision yesterday.
The test train, operating as train 912 today, went from Moncton down to Saint John and back.
Hopefully someone will get some good photos of old 2517 and the two blue test cars.
EDIT: here's a video from "John" aka cn8800!