Forest Protection Ltd. is the company responsible for providing the Air Tankers for New Brunswick. It's owned by the major forestry industry companies in the Province (ie. Irving, UPM, Fraser, etc.)
They are based out of Fredericton and Miramichi (my location) during the summer months.
They have a number of freqs licensed according to Industry Canada at the Fredericton Airport, nothing listed for Miramichi specifically but there's a possibility they're used Province-wide where possible.
Around here they use the primary traffic frequency (uncontrolled airport) and also have a discrete frequency or two when not in the immediate vicinity of an active airport. They also monitor the Departement of Natural Resources Simplex Channel 7 (172.260) freq. I rarely get a hit on any of the listed civil aviation freqs for Fredericton but they're likely used when out of my reception area so I can't be sure.
I'll provide a couple of links that may provide some idea where to look.
V/UHF
VHF Air