Shusher and Canonist are cards with situational advantages. Sometimes they do nothing but be 2/2, sometimes they are the bomb. So it makes perfect sense to cut one of each for 2 Worldly Tutors. Of course, the Tutor costs a turn and a card, but it is worth it if you can get the man you need. Additionally, you may now add some sort of creature toolbox so you can get better answers out of your Tutor. Like having a True Believer, Children of Korlis, Goldmeadow Harrier or Tracker (my favourite

). Not sure if this is the best way to play this deck, but at least it makes you less dependable on your topdecks.
Knight was very good. Big guys are good versus Fish and block Inkwells. Usually gets 8/8+. Can be used as card-drawing wall by EOT fetching Canopy, or just getting those Waste/Strip you need. Thinking about one or two Mishra's Factory so you can fetch more beats, or even Treetop Village.
First on the knight toolbox, I would not overextend with mishra and treetop. Wasteland for mana denial, Canopy for draw sounds enough. Adding more tools is not needed, waste and canopy are good enough on their own, knight makes them better plus knight answers a lot match ups making him good enough on its own as well, problem solved.
It seems to make perfect sense but it isn't. The problem is when you are facing combo that runs bounce effects you don't have the time to tutor up canonist. I said the tutr>shusher was good to break mana drain early on, or at least not walk into it. Tutor>Canonist could be too late in many situations. I could see Tutor>Knight/Tarm be a good play as well against aggro when the attrition war is about to end, both sides used up their fuel and neither side has a clear advantage, tarm/knight can be back breaking then. Another example versus Ichorid (thinking out of the box), say you run Jailer and you tutor for him. On paper it looks nice, it is top decked so they can't cabal/unmask it and it seems pretty fast (turn 2) to shut down dredge mechanic. I tested this with someone from this forum online. It was still not quick enough in most cases to really be worth it. I think addressing dredge in the side is still a little bit better when evaluating every factor.
My conclusion for now is that Tutor>Shusher is strong against mana drain. But if you run black then duress/thought is better overall. The tricky part is without running black why run tutors? And black has the best answers vs dredge. I would not go for tutors in G/W Beats even if it seems logical on paper. You need to play the tempo game more than any other deck, no real draw engine, no way to really come back once behind. So staying ahead and making every drop count right there right now is key. In what match ups is canonist and shusher truly dead anyway? Dredge and Stax I guess looking at the list and sb? Your match against stax isn't that bad at all in my opinion. And dredge I explained above, use SB. But when you DO need canonist, you don't have the luxury to tutor for him. Maybe you can do this:
2x Shusher
2x Wordly Tutor
3x Canonist
2x Knight
The knight isn't really that relevant early game. It is more of a mid game beat stick with utility that works well for long term games. Shusher is versus mana drain and you could get it with tutor so you have 4 in deck when the situation is present. I would not cut any canonist and if you do cut them all and find another way than tutor>canonist to deal with combo.