There were at least three, and surprisingly all on the same day (January 15, 1942), recorded losses of United States Army Air Force B-26's at Watson Lake. They were, however, most likely transitting across B.C. on their way to or from Alaska (my best guess) and not used for training purposes by Allied Forces. There is no record of any B-26 T.O.S. by the BCATP or RCAF in Canada. Watson Lake is also well known as the graveyard of the sole RCAF Lincoln bomber.
Here's the three B26's lost:
USAAF 40-1459, 40-1464, and 40-1501
Derek.