- Calgary's Heritage Park on May 4-5 and May 11-12
- Squamish's West Coast Railway Heritage Park on June 1-2 and June 9-10
- St. Thomas' Elgin County Railway Museum on July 19-21 and July 26-28
- Saint John on August 9-11 and August 16-18.
In Calgary, I assume they will go around the loop inside the Park. (FAQ)
In Saint John, the train will depart from Long Wharf (near Harbour Station) and cross the Reversing Falls bridge to behind Moosehead Breweries, then come back for a total of 24 minutes. They start departing at 9 AM and continue until 5 PM, so there will be plenty of opportunities to ride or photograph the train.
As far as I can tell, the host railroad provides the coaches and a diesel to do the actual work, and the Thomas engine provides the steam and photo opportunities. There will be plenty of other Thomas sights and activities at the site, including photo ops with Sir Topham Hatt™.
Here are a couple of videos showing Thomas at work. The first shows Thomas in St. Thomas, Ontario.
The second shows Thomas at the Gwili Steam Railway in Wales. He's smoking it up!
EDIT: Added some more dates.