On take off, fortunately, at low speed, the aircraft veered left.
Over the years, I've investigated a number of such events during takeoff - without exception they were due to thrust asymmetry - clearly obvious in N1/EPR splits when we checked the DFDR.
I worked 737 classics for a while - with the hydromechanical engine controls there is often miss-match in the engine accel rates which will give a thrust asymmetry during the takeoff throttle push. If memory serves, we determined it was appropriate to move the engine stabilization N1 higher prior to engaging the A/T (70% N1?) and the problem largely went away.
FADEC engines accel very uniformly, so that part of the issue is pretty much gone on the newer airplanes.
Since I've been working 747, we sometimes see "idle stagger", where the pilot - while gripping all four throttles - inadvertently staggering the throttles enough that one or more engines are above idle. When they advance the throttles, the engine(s) that are already above idle accel much quicker. The procedure of an A/T takeoff is to 'stand up' the throttles to obtain ~ 1.10 EPR or 40% N1, allow the engines to stabilize, then hit TOGA (or manually advance to TO). What I've seen is the pilots are occasionally careless about the 'stabilize' part, hitting TOGA before all four engines have caught up.
All that being said, it's unlikely to have anything to do with the Montreal event. I'm with Cockney - suspect crosswind/aquaplaning rather than a mechanical problem. I to have wondered about the lack of meaningful tread on aircraft tires...
Bluedonk, just curious, Rolls or Pratt on your 757?