I only use Fidelity , and from what I can see, they seem pretty competitive. yeah, Canadian, London & Australian exchanges have their own fees which are usually higher than trading a US stock. I suspect those will get passed on to you no matter which US broker you use.
“The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by an endless series of hobgoblins, most of them imaginary.” H. L. Mencken