Your soil bag should have a N-P-K value somewhere, maybe back? its nitrogen, potassium, phosphorous, dependsing on how much your soil has depends if you need to add some.
As far as buying some, I dont know what canadian tire or zellers would have sorry, Home depot/ lowes has stuff, go with fish emulsions if you cant afford the right nutrients. Or just a all purpose fert for veg and a bloom for flower something like, 5-3-1 would be good for veg 1-3-3 would be good for bloom. I use Fox farm grow big till about week 4 in flower of my grow and Foxfarm big bloom once it hits flower, i find with just bigbloom in flower it doesnt have enough nitrogen.
The way i remember NPK is N is for foilage P is for Roots and K is for Flowers. Not completely accurate with cannabis but just about with everything else, You want more N than P and K and more P than K in Veg, and Less N and about the same P and K for flowering. When you get about done DONT FORGET TO FLUSH. Flushing takes all the built up salts and some nutrients out of the soil so when you harvest you cant taste the fertilizers.
If you have any other questions or need any help PM me always willing to help a fellow growers. Good luck