I believe that canaries diets should consist of seeds, pellets and fresh food. I own 2 now and have owned 2 others in the past.
Mine get roughly 50/50 pellets and seed, and then get fruit and/or vegetables and greens clipped to the side of their cage daily.
I use the brand of seed Topflite since it is local to me but any varied, well known and fresh seed should be good. I prefer the seed that is not fortified with vitamins and whatnot and has only seeds, not dried vegetables or pellets, since often they don't eat these and the vitamins are wasted when the bird hulls it's seed. For pellets I use Roudybush, but most pellets will be alright. Harrisons, Labefers, Vetafarm, Higgins, to name a few. I like my pellets to be free of artificial colours or flavours and without added sugar, but whatever your bird will eat is fine. It is important that birds but both pellets and seed in my opinion, since the pellets will provide balanced nutrients that seeds lack and seeds are important since canaries are granivores and they need to have seed.
With the fresh food, just make it as varied as you can. Ordinary fruits and vegetables out of your fridge are fine, and if you have access to garden weeds that you know have no chemicals or anything on them those are great too. Dandelion, Sow thistle and Chickweed are the main ones I give mine out of my garden. Apple, Broccoli, Lettuce (but not Iceburg), carrot, pear, cucumber and many others are good fruits and vegetables, you can do some of your own research on what is safe and what isn't on the internet if you like. And always wash everything before giving it to your bird. I prefer whole pieces that I clip to the cage over chop, but that is personal preference. Fresh foods are just overall good for them, and it's nice for them mentally to have a varied diet as well.