CBC has a listing of some of the different regular events here:
Where and when to find food trucks this summer in Kitchener, Waterloo, Guelph
Food Truck Frenzy on Mondays seems pretty big. Here is
the schedule for Monday/Dunbar Food Trucks (I should plug that since it is in my neighbourhood). I'm pretty sure that there is a church somewhere in Kitchener that has a few trucks on Tuesday as well.
I really like
Truck Eats Cool Treats at Ambrosia Pastry, but I often go just for Ambrosia
I have mixed feelings about food trucks in Canada. There are a variety of factors at play, but in the US they seem to have a reputation of being good & cheap, in Canada there aren't many I've come across that qualify as cheap [for me, classified as meal & drink for under $10 after tax]. As for good, some are great and some are just OK.
Berlin-95 is one of my favourites (good if you like schnitzel & sausage) for quality & value, Crazy Canuck is also good for these. I also like West of Seoul and Cafe Du Monde for quality and they both stand out for being a little different from the meat/cheese/potato heavy trucks. I'm not a vegetarian, but I'd love to see more vegetarian options in the local trucks.