The robbery occurred when the bank was full of customers on Sunday afternoon.
Two armed men charged in and effectively "took over" the bank, police said on the weekend.
Police said one of the robbers vaulted a counter at the bank during the robbery.
But the robber ran into trouble when he came back over the counter — a 54-year-old male customer tackled him.
Police allege his partner, who was armed with a handgun, tried to shoot the customer but missed and struck a 22-year-old bank teller.
The same customer then chased the robbers into the parking lot, where the man with the handgun shot him.
Police said the two robbers fled the scene in a stolen Honda Civic, which was later found by investigators.
Arrest made last night
Toronto police Staff Insp. Mike Earl told reporters Tuesday that investigators believe the man they arrested in Brampton, Ont., on Monday evening is the robber who jumped over the counter at the bank.
"It was a smooth arrest," Earl said.
Andre Palmer, 26, faces several charges including robbery while armed with a firearm, attempted murder, aggravated assault and two counts of possession of stolen property, said Earl.
Palmer is due to appear in court this afternoon.
Earl said police have forensic evidence linking Palmer to the bank robbery, though he did not elaborate.
Palmer was also found with property "that was stolen from the bank," he said.
A description has been released of a second suspect police are still looking for. He was wearing jeans, a black Chicago White Sox baseball cap, a black hoodie with a white number eight on it and black shoes.
"Obviously this individual fired a loaded handgun in a bank robbery, injuring two people. We want to apprehend this guy as soon as possible," Earl said Tuesday.
The day after the robbery, police released images of the suspects and announced a $100,000 reward for information leading to their arrest and conviction.
On Tuesday, Earl said police already had dozens of tips pour in that investigators are now reviewing.