Toronto in the 1900s didn't much resemble the city we know today. Not only was the skyline virtually undeveloped—the tallest structures were the Temple Building at 10 storeys and the Trader's Bank Building at 15 storeys—but the Bloor Viaduct was yet to link the east and west sides of the city.
Old Union Station and the Yonge Street Wharf were still the main arrival points for the city, and Hanlan's Point was the place to be during the summer months.
On the flip side, what's now Old City Hall was already a towering and familiar presence, having been completed in 1899, and places like the St. Lawrence Market and the University of Toronto would be easily recognized by anyone able to travel back in time to that period.
In the 1900s, Toronto had a population of approximately 210,000 people, horses and carriages were still common on city streets, and the city suffered one of the worst fires in its history, losing almost all of the main commercial district (bounded by Bay, Wellington, Yonge, and Front Streets).
Here's what Toronto looked like through the 1900s.

Toronto skyline

Board of Trade Building

Cycling club

King Street
Weston Train Station

Avenue and Bloor

Eaton's factory interior

Laying asphalt on Elm Avenue

Jarvis Street

Entrance to U of T campus

Yonge looking north from Temperance

Fire aftermath

Fire aftermath

CNE midway

Candy department Eaton's

High Park

St. Lawrence Market

Toronto Ridings

Friday deals at Eaton's

Newsboy

Tally Ho showing visitors around the city

Toronto Harbour map

Crystal Palace (later destroyed by fire)

Sleighing at Queen's Park

St. George Street

Yonge and Front

Yonge Street Dock

Bookies at Woodbine Race Track (original)

Carriage ride

Cycling in Mimico

Flagpole painter looking west on Front

Hanlan's Point Hotel and Regatta

Bathurst north of St. Clair

Old (but then new) City Hall

Old Union Station

Diving Horse at Hanlan's Point

The Grange

Confederation Life Building

Yonge Street Warf

Yonge north of Bloor

Queen and James

Government House

Yonge and Queen

Dufferin Racetrack

University Avenue (with Queen's Park in the distance)

William Davies Store

Toronto Street

Collecting coal

Queen and Spadina

Ruins of Hanlan's Point Hotel
Toronto Archives and the WikiMedia Commons. Lead photo of cricket at Upper Canada College, 1908. With files from Derek Flack.