It shouldn't be difficult to fight if there is no clear notice of a speed change.
If there IS clear notice, juse say there was a large truck pulled over on the side of the road, blocking your view of the warning sign.
If you don't feel comfortable fighting this ticket, I suggest hiring a traffic ticket specialist.
There are companies out there devoted to just traffic tickets. such as "pointts".
I'm certain there will be a few companies in BC that could do it for ya.
Good luck!